chrome/browser/predictors/autocomplete_action_predictor.cc

   1 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #include "chrome/browser/predictors/autocomplete_action_predictor.h"
   6
   7 #include <math.h>
   8
   9 #include <vector>
  10
  11 #include "base/bind.h"
  12 #include "base/guid.h"
  13 #include "base/i18n/case_conversion.h"
  14 #include "base/metrics/histogram.h"
  15 #include "base/strings/string_util.h"
  16 #include "base/strings/stringprintf.h"
  17 #include "base/strings/utf_string_conversions.h"
  18 #include "chrome/browser/chrome_notification_types.h"
  19 #include "chrome/browser/history/history_service_factory.h"
  20 #include "chrome/browser/predictors/autocomplete_action_predictor_factory.h"
  21 #include "chrome/browser/predictors/predictor_database.h"
  22 #include "chrome/browser/predictors/predictor_database_factory.h"
  23 #include "chrome/browser/prerender/prerender_field_trial.h"
  24 #include "chrome/browser/prerender/prerender_handle.h"
  25 #include "chrome/browser/prerender/prerender_manager.h"
  26 #include "chrome/browser/prerender/prerender_manager_factory.h"
  27 #include "chrome/browser/profiles/profile.h"
  28 #include "chrome/browser/ui/omnibox/omnibox_popup_model.h"
  29 #include "components/history/core/browser/history_service.h"
  30 #include "components/history/core/browser/in_memory_database.h"
  31 #include "components/omnibox/autocomplete_match.h"
  32 #include "components/omnibox/autocomplete_result.h"
  33 #include "components/omnibox/omnibox_log.h"
  34 #include "content/public/browser/browser_thread.h"
  35 #include "content/public/browser/notification_details.h"
  36 #include "content/public/browser/notification_service.h"
  37 #include "content/public/browser/notification_source.h"
  38
  39 namespace {
  40
  41 const float kConfidenceCutoff[] = {
  42   0.8f,
  43   0.5f
  44 };
  45
  46 static_assert(arraysize(kConfidenceCutoff) ==
  47               predictors::AutocompleteActionPredictor::LAST_PREDICT_ACTION,
  48               "kConfidenceCutoff count should match LAST_PREDICT_ACTION");
  49
  50 const size_t kMinimumUserTextLength = 1;
  51 const int kMinimumNumberOfHits = 3;
  52
  53 enum DatabaseAction {
  54   DATABASE_ACTION_ADD,
  55   DATABASE_ACTION_UPDATE,
  56   DATABASE_ACTION_DELETE_SOME,
  57   DATABASE_ACTION_DELETE_ALL,
  58   DATABASE_ACTION_COUNT
  59 };
  60
  61 }  // namespace
  62
  63 namespace predictors {
  64
  65 const int AutocompleteActionPredictor::kMaximumDaysToKeepEntry = 14;
  66
  67 AutocompleteActionPredictor::AutocompleteActionPredictor(Profile* profile)
  68     : profile_(profile),
  69       main_profile_predictor_(NULL),
  70       incognito_predictor_(NULL),
  71       initialized_(false),
  72       history_service_observer_(this) {
  73   if (profile_->IsOffTheRecord()) {
  74     main_profile_predictor_ = AutocompleteActionPredictorFactory::GetForProfile(
  75         profile_->GetOriginalProfile());
  76     DCHECK(main_profile_predictor_);
  77     main_profile_predictor_->incognito_predictor_ = this;
  78     if (main_profile_predictor_->initialized_)
  79       CopyFromMainProfile();
  80   } else {
  81     // Request the in-memory database from the history to force it to load so
  82     // it's available as soon as possible.
  83     history::HistoryService* history_service =
  84         HistoryServiceFactory::GetForProfile(
  85             profile_, ServiceAccessType::EXPLICIT_ACCESS);
  86     if (history_service)
  87       history_service->InMemoryDatabase();
  88
  89     table_ =
  90         PredictorDatabaseFactory::GetForProfile(profile_)->autocomplete_table();
  91
  92     // Observe all main frame loads so we can wait for the first to complete
  93     // before accessing DB and IO threads to build the local cache.
  94     notification_registrar_.Add(this,
  95                                 content::NOTIFICATION_LOAD_COMPLETED_MAIN_FRAME,
  96                                 content::NotificationService::AllSources());
  97   }
  98 }
  99
 100 AutocompleteActionPredictor::~AutocompleteActionPredictor() {
 101   if (main_profile_predictor_)
 102     main_profile_predictor_->incognito_predictor_ = NULL;
 103   else if (incognito_predictor_)
 104     incognito_predictor_->main_profile_predictor_ = NULL;
 105   if (prerender_handle_.get())
 106     prerender_handle_->OnCancel();
 107 }
 108
 109 void AutocompleteActionPredictor::RegisterTransitionalMatches(
 110     const base::string16& user_text,
 111     const AutocompleteResult& result) {
 112   if (user_text.length() < kMinimumUserTextLength)
 113     return;
 114   const base::string16 lower_user_text(base::i18n::ToLower(user_text));
 115
 116   // Merge this in to an existing match if we already saw |user_text|
 117   std::vector<TransitionalMatch>::iterator match_it =
 118       std::find(transitional_matches_.begin(), transitional_matches_.end(),
 119                 lower_user_text);
 120
 121   if (match_it == transitional_matches_.end()) {
 122     TransitionalMatch transitional_match;
 123     transitional_match.user_text = lower_user_text;
 124     match_it = transitional_matches_.insert(transitional_matches_.end(),
 125                                             transitional_match);
 126   }
 127
 128   for (const auto& i : result) {
 129     if (std::find(match_it->urls.begin(), match_it->urls.end(),
 130                   i.destination_url) == match_it->urls.end()) {
 131       match_it->urls.push_back(i.destination_url);
 132     }
 133   }
 134 }
 135
 136 void AutocompleteActionPredictor::ClearTransitionalMatches() {
 137   transitional_matches_.clear();
 138 }
 139
 140 void AutocompleteActionPredictor::CancelPrerender() {
 141   // If the prerender has already been abandoned, leave it to its own timeout;
 142   // this normally gets called immediately after OnOmniboxOpenedUrl.
 143   if (prerender_handle_ && !prerender_handle_->IsAbandoned()) {
 144     prerender_handle_->OnCancel();
 145     prerender_handle_.reset();
 146   }
 147 }
 148
 149 void AutocompleteActionPredictor::StartPrerendering(
 150     const GURL& url,
 151     content::SessionStorageNamespace* session_storage_namespace,
 152     const gfx::Size& size) {
 153   // Only cancel the old prerender after starting the new one, so if the URLs
 154   // are the same, the underlying prerender will be reused.
 155   scoped_ptr<prerender::PrerenderHandle> old_prerender_handle(
 156       prerender_handle_.release());
 157   if (prerender::PrerenderManager* prerender_manager =
 158           prerender::PrerenderManagerFactory::GetForProfile(profile_)) {
 159     prerender_handle_.reset(prerender_manager->AddPrerenderFromOmnibox(
 160         url, session_storage_namespace, size));
 161   }
 162   if (old_prerender_handle)
 163     old_prerender_handle->OnCancel();
 164 }
 165
 166 // Given a match, return a recommended action.
 167 AutocompleteActionPredictor::Action
 168     AutocompleteActionPredictor::RecommendAction(
 169         const base::string16& user_text,
 170         const AutocompleteMatch& match) const {
 171   bool is_in_db = false;
 172   const double confidence = CalculateConfidence(user_text, match, &is_in_db);
 173   DCHECK(confidence >= 0.0 && confidence <= 1.0);
 174
 175   UMA_HISTOGRAM_BOOLEAN("AutocompleteActionPredictor.MatchIsInDb", is_in_db);
 176
 177   if (is_in_db) {
 178     // Multiple enties with the same URL are fine as the confidence may be
 179     // different.
 180     tracked_urls_.push_back(std::make_pair(match.destination_url, confidence));
 181     UMA_HISTOGRAM_COUNTS_100("AutocompleteActionPredictor.Confidence",
 182                              confidence * 100);
 183   }
 184
 185   // Map the confidence to an action.
 186   Action action = ACTION_NONE;
 187   for (int i = 0; i < LAST_PREDICT_ACTION; ++i) {
 188     if (confidence >= kConfidenceCutoff[i]) {
 189       action = static_cast<Action>(i);
 190       break;
 191     }
 192   }
 193
 194   // Downgrade prerender to preconnect if this is a search match or if omnibox
 195   // prerendering is disabled. There are cases when Instant will not handle a
 196   // search suggestion and in those cases it would be good to prerender the
 197   // search results, however search engines have not been set up to correctly
 198   // handle being prerendered and until they are we should avoid it.
 199   // http://crbug.com/117495
 200   if (action == ACTION_PRERENDER &&
 201       (AutocompleteMatch::IsSearchType(match.type) ||
 202        !prerender::IsOmniboxEnabled(profile_))) {
 203     action = ACTION_PRECONNECT;
 204   }
 205
 206   return action;
 207 }
 208
 209 // Return true if the suggestion type warrants a TCP/IP preconnection.
 210 // i.e., it is now quite likely that the user will select the related domain.
 211 // static
 212 bool AutocompleteActionPredictor::IsPreconnectable(
 213     const AutocompleteMatch& match) {
 214   return AutocompleteMatch::IsSearchType(match.type);
 215 }
 216
 217 bool AutocompleteActionPredictor::IsPrerenderAbandonedForTesting() {
 218   return prerender_handle_ && prerender_handle_->IsAbandoned();
 219 }
 220
 221 void AutocompleteActionPredictor::Observe(
 222     int type,
 223     const content::NotificationSource& source,
 224     const content::NotificationDetails& details) {
 225   switch (type) {
 226     case content::NOTIFICATION_LOAD_COMPLETED_MAIN_FRAME:
 227       CreateLocalCachesFromDatabase();
 228       notification_registrar_.Remove(
 229           this,
 230           content::NOTIFICATION_LOAD_COMPLETED_MAIN_FRAME,
 231           content::NotificationService::AllSources());
 232       break;
 233     case chrome::NOTIFICATION_OMNIBOX_OPENED_URL: {
 234       DCHECK(initialized_);
 235
 236       // TODO(dominich): This doesn't need to be synchronous. Investigate
 237       // posting it as a task to be run later.
 238       OnOmniboxOpenedUrl(*content::Details<OmniboxLog>(details).ptr());
 239       break;
 240     }
 241
 242     default:
 243       NOTREACHED() << "Unexpected notification observed.";
 244       break;
 245   }
 246 }
 247
 248 void AutocompleteActionPredictor::CreateLocalCachesFromDatabase() {
 249   // Create local caches using the database as loaded. We will garbage collect
 250   // rows from the caches and the database once the history service is
 251   // available.
 252   std::vector<AutocompleteActionPredictorTable::Row>* rows =
 253       new std::vector<AutocompleteActionPredictorTable::Row>();
 254   content::BrowserThread::PostTaskAndReply(content::BrowserThread::DB,
 255       FROM_HERE,
 256       base::Bind(&AutocompleteActionPredictorTable::GetAllRows, table_, rows),
 257       base::Bind(&AutocompleteActionPredictor::CreateCaches, AsWeakPtr(),
 258                  base::Owned(rows)));
 259 }
 260
 261 void AutocompleteActionPredictor::DeleteAllRows() {
 262   if (!initialized_)
 263     return;
 264
 265   db_cache_.clear();
 266   db_id_cache_.clear();
 267
 268   if (table_.get()) {
 269     content::BrowserThread::PostTask(content::BrowserThread::DB, FROM_HERE,
 270         base::Bind(&AutocompleteActionPredictorTable::DeleteAllRows,
 271                    table_));
 272   }
 273
 274   UMA_HISTOGRAM_ENUMERATION("AutocompleteActionPredictor.DatabaseAction",
 275                             DATABASE_ACTION_DELETE_ALL, DATABASE_ACTION_COUNT);
 276 }
 277
 278 void AutocompleteActionPredictor::DeleteRowsWithURLs(
 279     const history::URLRows& rows) {
 280   if (!initialized_)
 281     return;
 282
 283   std::vector<AutocompleteActionPredictorTable::Row::Id> id_list;
 284
 285   for (DBCacheMap::iterator it = db_cache_.begin(); it != db_cache_.end();) {
 286     if (std::find_if(rows.begin(), rows.end(),
 287         history::URLRow::URLRowHasURL(it->first.url)) != rows.end()) {
 288       const DBIdCacheMap::iterator id_it = db_id_cache_.find(it->first);
 289       DCHECK(id_it != db_id_cache_.end());
 290       id_list.push_back(id_it->second);
 291       db_id_cache_.erase(id_it);
 292       db_cache_.erase(it++);
 293     } else {
 294       ++it;
 295     }
 296   }
 297
 298   if (table_.get()) {
 299     content::BrowserThread::PostTask(content::BrowserThread::DB, FROM_HERE,
 300         base::Bind(&AutocompleteActionPredictorTable::DeleteRows, table_,
 301                    id_list));
 302   }
 303
 304   UMA_HISTOGRAM_ENUMERATION("AutocompleteActionPredictor.DatabaseAction",
 305                             DATABASE_ACTION_DELETE_SOME, DATABASE_ACTION_COUNT);
 306 }
 307
 308 void AutocompleteActionPredictor::OnOmniboxOpenedUrl(const OmniboxLog& log) {
 309   if (log.text.length() < kMinimumUserTextLength)
 310     return;
 311
 312   // Do not attempt to learn from omnibox interactions where the omnibox
 313   // dropdown is closed.  In these cases the user text (|log.text|) that we
 314   // learn from is either empty or effectively identical to the destination
 315   // string.  In either case, it can't teach us much.  Also do not attempt
 316   // to learn from paste-and-go actions even if the popup is open because
 317   // the paste-and-go destination has no relation to whatever text the user
 318   // may have typed.
 319   if (!log.is_popup_open || log.is_paste_and_go)
 320     return;
 321
 322   // Abandon the current prerender. If it is to be used, it will be used very
 323   // soon, so use the lower timeout.
 324   if (prerender_handle_) {
 325     prerender_handle_->OnNavigateAway();
 326     // Don't release |prerender_handle_| so it is canceled if it survives to the
 327     // next StartPrerendering call.
 328   }
 329
 330   UMA_HISTOGRAM_BOOLEAN(
 331       base::StringPrintf("Prerender.OmniboxNavigationsCouldPrerender%s",
 332                          prerender::PrerenderManager::GetModeString()).c_str(),
 333       prerender::IsOmniboxEnabled(profile_));
 334
 335   const AutocompleteMatch& match = log.result.match_at(log.selected_index);
 336   const GURL& opened_url = match.destination_url;
 337   const base::string16 lower_user_text(base::i18n::ToLower(log.text));
 338
 339   // Traverse transitional matches for those that have a user_text that is a
 340   // prefix of |lower_user_text|.
 341   std::vector<AutocompleteActionPredictorTable::Row> rows_to_add;
 342   std::vector<AutocompleteActionPredictorTable::Row> rows_to_update;
 343
 344   for (std::vector<TransitionalMatch>::const_iterator it =
 345         transitional_matches_.begin(); it != transitional_matches_.end();
 346         ++it) {
 347     if (!base::StartsWith(lower_user_text, it->user_text, true))
 348       continue;
 349
 350     // Add entries to the database for those matches.
 351     for (std::vector<GURL>::const_iterator url_it = it->urls.begin();
 352           url_it != it->urls.end(); ++url_it) {
 353       DCHECK(it->user_text.length() >= kMinimumUserTextLength);
 354       const DBCacheKey key = { it->user_text, *url_it };
 355       const bool is_hit = (*url_it == opened_url);
 356
 357       AutocompleteActionPredictorTable::Row row;
 358       row.user_text = key.user_text;
 359       row.url = key.url;
 360
 361       DBCacheMap::iterator it = db_cache_.find(key);
 362       if (it == db_cache_.end()) {
 363         row.id = base::GenerateGUID();
 364         row.number_of_hits = is_hit ? 1 : 0;
 365         row.number_of_misses = is_hit ? 0 : 1;
 366
 367         rows_to_add.push_back(row);
 368       } else {
 369         DCHECK(db_id_cache_.find(key) != db_id_cache_.end());
 370         row.id = db_id_cache_.find(key)->second;
 371         row.number_of_hits = it->second.number_of_hits + (is_hit ? 1 : 0);
 372         row.number_of_misses = it->second.number_of_misses + (is_hit ? 0 : 1);
 373
 374         rows_to_update.push_back(row);
 375       }
 376     }
 377   }
 378   if (rows_to_add.size() > 0 || rows_to_update.size() > 0)
 379     AddAndUpdateRows(rows_to_add, rows_to_update);
 380
 381   ClearTransitionalMatches();
 382
 383   // Check against tracked urls and log accuracy for the confidence we
 384   // predicted.
 385   for (std::vector<std::pair<GURL, double> >::const_iterator it =
 386        tracked_urls_.begin(); it != tracked_urls_.end();
 387        ++it) {
 388     if (opened_url == it->first) {
 389       UMA_HISTOGRAM_COUNTS_100("AutocompleteActionPredictor.AccurateCount",
 390                                it->second * 100);
 391     }
 392   }
 393   tracked_urls_.clear();
 394 }
 395
 396 void AutocompleteActionPredictor::AddAndUpdateRows(
 397     const AutocompleteActionPredictorTable::Rows& rows_to_add,
 398     const AutocompleteActionPredictorTable::Rows& rows_to_update) {
 399   if (!initialized_)
 400     return;
 401
 402   for (AutocompleteActionPredictorTable::Rows::const_iterator it =
 403        rows_to_add.begin(); it != rows_to_add.end(); ++it) {
 404     const DBCacheKey key = { it->user_text, it->url };
 405     DBCacheValue value = { it->number_of_hits, it->number_of_misses };
 406
 407     DCHECK(db_cache_.find(key) == db_cache_.end());
 408
 409     db_cache_[key] = value;
 410     db_id_cache_[key] = it->id;
 411     UMA_HISTOGRAM_ENUMERATION("AutocompleteActionPredictor.DatabaseAction",
 412                               DATABASE_ACTION_ADD, DATABASE_ACTION_COUNT);
 413   }
 414   for (AutocompleteActionPredictorTable::Rows::const_iterator it =
 415        rows_to_update.begin(); it != rows_to_update.end(); ++it) {
 416     const DBCacheKey key = { it->user_text, it->url };
 417
 418     DBCacheMap::iterator db_it = db_cache_.find(key);
 419     DCHECK(db_it != db_cache_.end());
 420     DCHECK(db_id_cache_.find(key) != db_id_cache_.end());
 421
 422     db_it->second.number_of_hits = it->number_of_hits;
 423     db_it->second.number_of_misses = it->number_of_misses;
 424     UMA_HISTOGRAM_ENUMERATION("AutocompleteActionPredictor.DatabaseAction",
 425                               DATABASE_ACTION_UPDATE, DATABASE_ACTION_COUNT);
 426   }
 427
 428   if (table_.get()) {
 429     content::BrowserThread::PostTask(content::BrowserThread::DB, FROM_HERE,
 430         base::Bind(&AutocompleteActionPredictorTable::AddAndUpdateRows,
 431                    table_, rows_to_add, rows_to_update));
 432   }
 433 }
 434
 435 void AutocompleteActionPredictor::CreateCaches(
 436     std::vector<AutocompleteActionPredictorTable::Row>* rows) {
 437   CHECK(content::BrowserThread::CurrentlyOn(content::BrowserThread::UI));
 438   DCHECK(!profile_->IsOffTheRecord());
 439   DCHECK(!initialized_);
 440   DCHECK(db_cache_.empty());
 441   DCHECK(db_id_cache_.empty());
 442
 443   for (std::vector<AutocompleteActionPredictorTable::Row>::const_iterator it =
 444        rows->begin(); it != rows->end(); ++it) {
 445     const DBCacheKey key = { it->user_text, it->url };
 446     const DBCacheValue value = { it->number_of_hits, it->number_of_misses };
 447     db_cache_[key] = value;
 448     db_id_cache_[key] = it->id;
 449   }
 450
 451   // If the history service is ready, delete any old or invalid entries.
 452   history::HistoryService* history_service =
 453       HistoryServiceFactory::GetForProfile(profile_,
 454                                            ServiceAccessType::EXPLICIT_ACCESS);
 455   if (!TryDeleteOldEntries(history_service)) {
 456     // Wait for the notification that the history service is ready and the URL
 457     // DB is loaded.
 458     if (history_service)
 459       history_service_observer_.Add(history_service);
 460   }
 461 }
 462
 463 bool AutocompleteActionPredictor::TryDeleteOldEntries(
 464     history::HistoryService* service) {
 465   CHECK(content::BrowserThread::CurrentlyOn(content::BrowserThread::UI));
 466   DCHECK(!profile_->IsOffTheRecord());
 467   DCHECK(!initialized_);
 468
 469   if (!service)
 470     return false;
 471
 472   history::URLDatabase* url_db = service->InMemoryDatabase();
 473   if (!url_db)
 474     return false;
 475
 476   DeleteOldEntries(url_db);
 477   return true;
 478 }
 479
 480 void AutocompleteActionPredictor::DeleteOldEntries(
 481     history::URLDatabase* url_db) {
 482   CHECK(content::BrowserThread::CurrentlyOn(content::BrowserThread::UI));
 483   DCHECK(!profile_->IsOffTheRecord());
 484   DCHECK(!initialized_);
 485   DCHECK(table_.get());
 486
 487   std::vector<AutocompleteActionPredictorTable::Row::Id> ids_to_delete;
 488   DeleteOldIdsFromCaches(url_db, &ids_to_delete);
 489
 490   content::BrowserThread::PostTask(content::BrowserThread::DB, FROM_HERE,
 491       base::Bind(&AutocompleteActionPredictorTable::DeleteRows, table_,
 492                  ids_to_delete));
 493
 494   FinishInitialization();
 495   if (incognito_predictor_)
 496     incognito_predictor_->CopyFromMainProfile();
 497 }
 498
 499 void AutocompleteActionPredictor::DeleteOldIdsFromCaches(
 500     history::URLDatabase* url_db,
 501     std::vector<AutocompleteActionPredictorTable::Row::Id>* id_list) {
 502   CHECK(content::BrowserThread::CurrentlyOn(content::BrowserThread::UI));
 503   DCHECK(!profile_->IsOffTheRecord());
 504   DCHECK(!initialized_);
 505   DCHECK(url_db);
 506   DCHECK(id_list);
 507
 508   id_list->clear();
 509   for (DBCacheMap::iterator it = db_cache_.begin(); it != db_cache_.end();) {
 510     history::URLRow url_row;
 511
 512     if ((url_db->GetRowForURL(it->first.url, &url_row) == 0) ||
 513         ((base::Time::Now() - url_row.last_visit()).InDays() >
 514          kMaximumDaysToKeepEntry)) {
 515       const DBIdCacheMap::iterator id_it = db_id_cache_.find(it->first);
 516       DCHECK(id_it != db_id_cache_.end());
 517       id_list->push_back(id_it->second);
 518       db_id_cache_.erase(id_it);
 519       db_cache_.erase(it++);
 520     } else {
 521       ++it;
 522     }
 523   }
 524 }
 525
 526 void AutocompleteActionPredictor::CopyFromMainProfile() {
 527   CHECK(content::BrowserThread::CurrentlyOn(content::BrowserThread::UI));
 528   DCHECK(profile_->IsOffTheRecord());
 529   DCHECK(!initialized_);
 530   DCHECK(main_profile_predictor_);
 531   DCHECK(main_profile_predictor_->initialized_);
 532
 533   db_cache_ = main_profile_predictor_->db_cache_;
 534   db_id_cache_ = main_profile_predictor_->db_id_cache_;
 535   FinishInitialization();
 536 }
 537
 538 void AutocompleteActionPredictor::FinishInitialization() {
 539   CHECK(content::BrowserThread::CurrentlyOn(content::BrowserThread::UI));
 540   DCHECK(!initialized_);
 541
 542   // Incognito and normal profiles should listen only to omnibox notifications
 543   // from their own profile, but both should listen to history deletions from
 544   // the main profile, since opening the history page in either case actually
 545   // opens the non-incognito history (and lets users delete from there).
 546   notification_registrar_.Add(this, chrome::NOTIFICATION_OMNIBOX_OPENED_URL,
 547                               content::Source<Profile>(profile_));
 548   initialized_ = true;
 549 }
 550
 551 double AutocompleteActionPredictor::CalculateConfidence(
 552     const base::string16& user_text,
 553     const AutocompleteMatch& match,
 554     bool* is_in_db) const {
 555   const DBCacheKey key = { user_text, match.destination_url };
 556
 557   *is_in_db = false;
 558   if (user_text.length() < kMinimumUserTextLength)
 559     return 0.0;
 560
 561   const DBCacheMap::const_iterator iter = db_cache_.find(key);
 562   if (iter == db_cache_.end())
 563     return 0.0;
 564
 565   *is_in_db = true;
 566   return CalculateConfidenceForDbEntry(iter);
 567 }
 568
 569 double AutocompleteActionPredictor::CalculateConfidenceForDbEntry(
 570     DBCacheMap::const_iterator iter) const {
 571   const DBCacheValue& value = iter->second;
 572   if (value.number_of_hits < kMinimumNumberOfHits)
 573     return 0.0;
 574
 575   const double number_of_hits = static_cast<double>(value.number_of_hits);
 576   return number_of_hits / (number_of_hits + value.number_of_misses);
 577 }
 578
 579 void AutocompleteActionPredictor::Shutdown() {
 580   history_service_observer_.RemoveAll();
 581 }
 582
 583 void AutocompleteActionPredictor::OnURLsDeleted(
 584     history::HistoryService* history_service,
 585     bool all_history,
 586     bool expired,
 587     const history::URLRows& deleted_rows,
 588     const std::set<GURL>& favicon_urls) {
 589   if (!initialized_)
 590     return;
 591
 592   if (all_history)
 593     DeleteAllRows();
 594   else
 595     DeleteRowsWithURLs(deleted_rows);
 596 }
 597
 598 void AutocompleteActionPredictor::OnHistoryServiceLoaded(
 599     history::HistoryService* history_service) {
 600   TryDeleteOldEntries(history_service);
 601   history_service_observer_.Remove(history_service);
 602 }
 603
 604 AutocompleteActionPredictor::TransitionalMatch::TransitionalMatch() {
 605 }
 606
 607 AutocompleteActionPredictor::TransitionalMatch::~TransitionalMatch() {
 608 }
 609
 610 }  // namespace predictors