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 "components/history/core/browser/history_service.h"
  29 #include "components/history/core/browser/in_memory_database.h"
  30 #include "components/omnibox/browser/autocomplete_match.h"
  31 #include "components/omnibox/browser/autocomplete_result.h"
  32 #include "components/omnibox/browser/omnibox_log.h"
  33 #include "components/omnibox/browser/omnibox_popup_model.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::OnOmniboxOpenedUrl(const OmniboxLog& log) {
 222   if (!initialized_)
 223     return;
 224
 225   // TODO(dominich): The body of this method doesn't need to be run
 226   // synchronously. Investigate posting it as a task to be run later.
 227
 228   if (log.text.length() < kMinimumUserTextLength)
 229     return;
 230
 231   // Do not attempt to learn from omnibox interactions where the omnibox
 232   // dropdown is closed.  In these cases the user text (|log.text|) that we
 233   // learn from is either empty or effectively identical to the destination
 234   // string.  In either case, it can't teach us much.  Also do not attempt
 235   // to learn from paste-and-go actions even if the popup is open because
 236   // the paste-and-go destination has no relation to whatever text the user
 237   // may have typed.
 238   if (!log.is_popup_open || log.is_paste_and_go)
 239     return;
 240
 241   // Abandon the current prerender. If it is to be used, it will be used very
 242   // soon, so use the lower timeout.
 243   if (prerender_handle_) {
 244     prerender_handle_->OnNavigateAway();
 245     // Don't release |prerender_handle_| so it is canceled if it survives to the
 246     // next StartPrerendering call.
 247   }
 248
 249   UMA_HISTOGRAM_BOOLEAN(
 250       base::StringPrintf("Prerender.OmniboxNavigationsCouldPrerender%s",
 251                          prerender::PrerenderManager::GetModeString()).c_str(),
 252       prerender::IsOmniboxEnabled(profile_));
 253
 254   const AutocompleteMatch& match = log.result.match_at(log.selected_index);
 255   const GURL& opened_url = match.destination_url;
 256   const base::string16 lower_user_text(base::i18n::ToLower(log.text));
 257
 258   // Traverse transitional matches for those that have a user_text that is a
 259   // prefix of |lower_user_text|.
 260   std::vector<AutocompleteActionPredictorTable::Row> rows_to_add;
 261   std::vector<AutocompleteActionPredictorTable::Row> rows_to_update;
 262
 263   for (std::vector<TransitionalMatch>::const_iterator it =
 264         transitional_matches_.begin(); it != transitional_matches_.end();
 265         ++it) {
 266     if (!base::StartsWith(lower_user_text, it->user_text,
 267                           base::CompareCase::SENSITIVE))
 268       continue;
 269
 270     // Add entries to the database for those matches.
 271     for (std::vector<GURL>::const_iterator url_it = it->urls.begin();
 272           url_it != it->urls.end(); ++url_it) {
 273       DCHECK(it->user_text.length() >= kMinimumUserTextLength);
 274       const DBCacheKey key = { it->user_text, *url_it };
 275       const bool is_hit = (*url_it == opened_url);
 276
 277       AutocompleteActionPredictorTable::Row row;
 278       row.user_text = key.user_text;
 279       row.url = key.url;
 280
 281       DBCacheMap::iterator it = db_cache_.find(key);
 282       if (it == db_cache_.end()) {
 283         row.id = base::GenerateGUID();
 284         row.number_of_hits = is_hit ? 1 : 0;
 285         row.number_of_misses = is_hit ? 0 : 1;
 286
 287         rows_to_add.push_back(row);
 288       } else {
 289         DCHECK(db_id_cache_.find(key) != db_id_cache_.end());
 290         row.id = db_id_cache_.find(key)->second;
 291         row.number_of_hits = it->second.number_of_hits + (is_hit ? 1 : 0);
 292         row.number_of_misses = it->second.number_of_misses + (is_hit ? 0 : 1);
 293
 294         rows_to_update.push_back(row);
 295       }
 296     }
 297   }
 298   if (rows_to_add.size() > 0 || rows_to_update.size() > 0)
 299     AddAndUpdateRows(rows_to_add, rows_to_update);
 300
 301   ClearTransitionalMatches();
 302
 303   // Check against tracked urls and log accuracy for the confidence we
 304   // predicted.
 305   for (std::vector<std::pair<GURL, double> >::const_iterator it =
 306        tracked_urls_.begin(); it != tracked_urls_.end();
 307        ++it) {
 308     if (opened_url == it->first) {
 309       UMA_HISTOGRAM_COUNTS_100("AutocompleteActionPredictor.AccurateCount",
 310                                it->second * 100);
 311     }
 312   }
 313   tracked_urls_.clear();
 314 }
 315
 316 void AutocompleteActionPredictor::Observe(
 317     int type,
 318     const content::NotificationSource& source,
 319     const content::NotificationDetails& details) {
 320   DCHECK_EQ(content::NOTIFICATION_LOAD_COMPLETED_MAIN_FRAME, type);
 321   CreateLocalCachesFromDatabase();
 322   notification_registrar_.Remove(
 323       this, content::NOTIFICATION_LOAD_COMPLETED_MAIN_FRAME,
 324       content::NotificationService::AllSources());
 325 }
 326
 327 void AutocompleteActionPredictor::CreateLocalCachesFromDatabase() {
 328   // Create local caches using the database as loaded. We will garbage collect
 329   // rows from the caches and the database once the history service is
 330   // available.
 331   std::vector<AutocompleteActionPredictorTable::Row>* rows =
 332       new std::vector<AutocompleteActionPredictorTable::Row>();
 333   content::BrowserThread::PostTaskAndReply(
 334       content::BrowserThread::DB, FROM_HERE,
 335       base::Bind(&AutocompleteActionPredictorTable::GetAllRows, table_, rows),
 336       base::Bind(&AutocompleteActionPredictor::CreateCaches, AsWeakPtr(),
 337                  base::Owned(rows)));
 338 }
 339
 340 void AutocompleteActionPredictor::DeleteAllRows() {
 341   if (!initialized_)
 342     return;
 343
 344   db_cache_.clear();
 345   db_id_cache_.clear();
 346
 347   if (table_.get()) {
 348     content::BrowserThread::PostTask(
 349         content::BrowserThread::DB, FROM_HERE,
 350         base::Bind(&AutocompleteActionPredictorTable::DeleteAllRows, table_));
 351   }
 352
 353   UMA_HISTOGRAM_ENUMERATION("AutocompleteActionPredictor.DatabaseAction",
 354                             DATABASE_ACTION_DELETE_ALL, DATABASE_ACTION_COUNT);
 355 }
 356
 357 void AutocompleteActionPredictor::DeleteRowsWithURLs(
 358     const history::URLRows& rows) {
 359   if (!initialized_)
 360     return;
 361
 362   std::vector<AutocompleteActionPredictorTable::Row::Id> id_list;
 363
 364   for (DBCacheMap::iterator it = db_cache_.begin(); it != db_cache_.end();) {
 365     if (std::find_if(rows.begin(), rows.end(),
 366                      history::URLRow::URLRowHasURL(it->first.url)) !=
 367         rows.end()) {
 368       const DBIdCacheMap::iterator id_it = db_id_cache_.find(it->first);
 369       DCHECK(id_it != db_id_cache_.end());
 370       id_list.push_back(id_it->second);
 371       db_id_cache_.erase(id_it);
 372       db_cache_.erase(it++);
 373     } else {
 374       ++it;
 375     }
 376   }
 377
 378   if (table_.get()) {
 379     content::BrowserThread::PostTask(
 380         content::BrowserThread::DB, FROM_HERE,
 381         base::Bind(&AutocompleteActionPredictorTable::DeleteRows, table_,
 382                    id_list));
 383   }
 384
 385   UMA_HISTOGRAM_ENUMERATION("AutocompleteActionPredictor.DatabaseAction",
 386                             DATABASE_ACTION_DELETE_SOME, DATABASE_ACTION_COUNT);
 387 }
 388
 389 void AutocompleteActionPredictor::AddAndUpdateRows(
 390     const AutocompleteActionPredictorTable::Rows& rows_to_add,
 391     const AutocompleteActionPredictorTable::Rows& rows_to_update) {
 392   if (!initialized_)
 393     return;
 394
 395   for (AutocompleteActionPredictorTable::Rows::const_iterator it =
 396        rows_to_add.begin(); it != rows_to_add.end(); ++it) {
 397     const DBCacheKey key = { it->user_text, it->url };
 398     DBCacheValue value = { it->number_of_hits, it->number_of_misses };
 399
 400     DCHECK(db_cache_.find(key) == db_cache_.end());
 401
 402     db_cache_[key] = value;
 403     db_id_cache_[key] = it->id;
 404     UMA_HISTOGRAM_ENUMERATION("AutocompleteActionPredictor.DatabaseAction",
 405                               DATABASE_ACTION_ADD, DATABASE_ACTION_COUNT);
 406   }
 407   for (AutocompleteActionPredictorTable::Rows::const_iterator it =
 408        rows_to_update.begin(); it != rows_to_update.end(); ++it) {
 409     const DBCacheKey key = { it->user_text, it->url };
 410
 411     DBCacheMap::iterator db_it = db_cache_.find(key);
 412     DCHECK(db_it != db_cache_.end());
 413     DCHECK(db_id_cache_.find(key) != db_id_cache_.end());
 414
 415     db_it->second.number_of_hits = it->number_of_hits;
 416     db_it->second.number_of_misses = it->number_of_misses;
 417     UMA_HISTOGRAM_ENUMERATION("AutocompleteActionPredictor.DatabaseAction",
 418                               DATABASE_ACTION_UPDATE, DATABASE_ACTION_COUNT);
 419   }
 420
 421   if (table_.get()) {
 422     content::BrowserThread::PostTask(content::BrowserThread::DB, FROM_HERE,
 423         base::Bind(&AutocompleteActionPredictorTable::AddAndUpdateRows,
 424                    table_, rows_to_add, rows_to_update));
 425   }
 426 }
 427
 428 void AutocompleteActionPredictor::CreateCaches(
 429     std::vector<AutocompleteActionPredictorTable::Row>* rows) {
 430   CHECK(content::BrowserThread::CurrentlyOn(content::BrowserThread::UI));
 431   DCHECK(!profile_->IsOffTheRecord());
 432   DCHECK(!initialized_);
 433   DCHECK(db_cache_.empty());
 434   DCHECK(db_id_cache_.empty());
 435
 436   for (std::vector<AutocompleteActionPredictorTable::Row>::const_iterator it =
 437        rows->begin(); it != rows->end(); ++it) {
 438     const DBCacheKey key = { it->user_text, it->url };
 439     const DBCacheValue value = { it->number_of_hits, it->number_of_misses };
 440     db_cache_[key] = value;
 441     db_id_cache_[key] = it->id;
 442   }
 443
 444   // If the history service is ready, delete any old or invalid entries.
 445   history::HistoryService* history_service =
 446       HistoryServiceFactory::GetForProfile(profile_,
 447                                            ServiceAccessType::EXPLICIT_ACCESS);
 448   if (!TryDeleteOldEntries(history_service)) {
 449     // Wait for the notification that the history service is ready and the URL
 450     // DB is loaded.
 451     if (history_service)
 452       history_service_observer_.Add(history_service);
 453   }
 454 }
 455
 456 bool AutocompleteActionPredictor::TryDeleteOldEntries(
 457     history::HistoryService* service) {
 458   CHECK(content::BrowserThread::CurrentlyOn(content::BrowserThread::UI));
 459   DCHECK(!profile_->IsOffTheRecord());
 460   DCHECK(!initialized_);
 461
 462   if (!service)
 463     return false;
 464
 465   history::URLDatabase* url_db = service->InMemoryDatabase();
 466   if (!url_db)
 467     return false;
 468
 469   DeleteOldEntries(url_db);
 470   return true;
 471 }
 472
 473 void AutocompleteActionPredictor::DeleteOldEntries(
 474     history::URLDatabase* url_db) {
 475   CHECK(content::BrowserThread::CurrentlyOn(content::BrowserThread::UI));
 476   DCHECK(!profile_->IsOffTheRecord());
 477   DCHECK(!initialized_);
 478   DCHECK(table_.get());
 479
 480   std::vector<AutocompleteActionPredictorTable::Row::Id> ids_to_delete;
 481   DeleteOldIdsFromCaches(url_db, &ids_to_delete);
 482
 483   content::BrowserThread::PostTask(content::BrowserThread::DB, FROM_HERE,
 484       base::Bind(&AutocompleteActionPredictorTable::DeleteRows, table_,
 485                  ids_to_delete));
 486
 487   FinishInitialization();
 488   if (incognito_predictor_)
 489     incognito_predictor_->CopyFromMainProfile();
 490 }
 491
 492 void AutocompleteActionPredictor::DeleteOldIdsFromCaches(
 493     history::URLDatabase* url_db,
 494     std::vector<AutocompleteActionPredictorTable::Row::Id>* id_list) {
 495   CHECK(content::BrowserThread::CurrentlyOn(content::BrowserThread::UI));
 496   DCHECK(!profile_->IsOffTheRecord());
 497   DCHECK(!initialized_);
 498   DCHECK(url_db);
 499   DCHECK(id_list);
 500
 501   id_list->clear();
 502   for (DBCacheMap::iterator it = db_cache_.begin(); it != db_cache_.end();) {
 503     history::URLRow url_row;
 504
 505     if ((url_db->GetRowForURL(it->first.url, &url_row) == 0) ||
 506         ((base::Time::Now() - url_row.last_visit()).InDays() >
 507          kMaximumDaysToKeepEntry)) {
 508       const DBIdCacheMap::iterator id_it = db_id_cache_.find(it->first);
 509       DCHECK(id_it != db_id_cache_.end());
 510       id_list->push_back(id_it->second);
 511       db_id_cache_.erase(id_it);
 512       db_cache_.erase(it++);
 513     } else {
 514       ++it;
 515     }
 516   }
 517 }
 518
 519 void AutocompleteActionPredictor::CopyFromMainProfile() {
 520   CHECK(content::BrowserThread::CurrentlyOn(content::BrowserThread::UI));
 521   DCHECK(profile_->IsOffTheRecord());
 522   DCHECK(!initialized_);
 523   DCHECK(main_profile_predictor_);
 524   DCHECK(main_profile_predictor_->initialized_);
 525
 526   db_cache_ = main_profile_predictor_->db_cache_;
 527   db_id_cache_ = main_profile_predictor_->db_id_cache_;
 528   FinishInitialization();
 529 }
 530
 531 void AutocompleteActionPredictor::FinishInitialization() {
 532   CHECK(content::BrowserThread::CurrentlyOn(content::BrowserThread::UI));
 533   DCHECK(!initialized_);
 534   initialized_ = true;
 535 }
 536
 537 double AutocompleteActionPredictor::CalculateConfidence(
 538     const base::string16& user_text,
 539     const AutocompleteMatch& match,
 540     bool* is_in_db) const {
 541   const DBCacheKey key = { user_text, match.destination_url };
 542
 543   *is_in_db = false;
 544   if (user_text.length() < kMinimumUserTextLength)
 545     return 0.0;
 546
 547   const DBCacheMap::const_iterator iter = db_cache_.find(key);
 548   if (iter == db_cache_.end())
 549     return 0.0;
 550
 551   *is_in_db = true;
 552   return CalculateConfidenceForDbEntry(iter);
 553 }
 554
 555 double AutocompleteActionPredictor::CalculateConfidenceForDbEntry(
 556     DBCacheMap::const_iterator iter) const {
 557   const DBCacheValue& value = iter->second;
 558   if (value.number_of_hits < kMinimumNumberOfHits)
 559     return 0.0;
 560
 561   const double number_of_hits = static_cast<double>(value.number_of_hits);
 562   return number_of_hits / (number_of_hits + value.number_of_misses);
 563 }
 564
 565 void AutocompleteActionPredictor::Shutdown() {
 566   history_service_observer_.RemoveAll();
 567 }
 568
 569 void AutocompleteActionPredictor::OnURLsDeleted(
 570     history::HistoryService* history_service,
 571     bool all_history,
 572     bool expired,
 573     const history::URLRows& deleted_rows,
 574     const std::set<GURL>& favicon_urls) {
 575   if (!initialized_)
 576     return;
 577
 578   if (all_history)
 579     DeleteAllRows();
 580   else
 581     DeleteRowsWithURLs(deleted_rows);
 582 }
 583
 584 void AutocompleteActionPredictor::OnHistoryServiceLoaded(
 585     history::HistoryService* history_service) {
 586   TryDeleteOldEntries(history_service);
 587   history_service_observer_.Remove(history_service);
 588 }
 589
 590 AutocompleteActionPredictor::TransitionalMatch::TransitionalMatch() {
 591 }
 592
 593 AutocompleteActionPredictor::TransitionalMatch::~TransitionalMatch() {
 594 }
 595
 596 }  // namespace predictors