ash/drag_drop/drag_drop_controller.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 "ash/drag_drop/drag_drop_controller.h"
   6
   7 #include "ash/drag_drop/drag_drop_tracker.h"
   8 #include "ash/drag_drop/drag_image_view.h"
   9 #include "ash/shell.h"
  10 #include "base/bind.h"
  11 #include "base/message_loop/message_loop.h"
  12 #include "base/metrics/histogram_macros.h"
  13 #include "base/run_loop.h"
  14 #include "ui/aura/client/capture_client.h"
  15 #include "ui/aura/env.h"
  16 #include "ui/aura/window.h"
  17 #include "ui/aura/window_delegate.h"
  18 #include "ui/aura/window_event_dispatcher.h"
  19 #include "ui/base/dragdrop/drag_drop_types.h"
  20 #include "ui/base/dragdrop/os_exchange_data.h"
  21 #include "ui/base/hit_test.h"
  22 #include "ui/events/event.h"
  23 #include "ui/events/event_utils.h"
  24 #include "ui/gfx/animation/linear_animation.h"
  25 #include "ui/gfx/geometry/point.h"
  26 #include "ui/gfx/geometry/rect.h"
  27 #include "ui/gfx/geometry/rect_conversions.h"
  28 #include "ui/gfx/path.h"
  29 #include "ui/views/views_delegate.h"
  30 #include "ui/views/widget/native_widget_aura.h"
  31 #include "ui/wm/core/coordinate_conversion.h"
  32 #include "ui/wm/public/drag_drop_delegate.h"
  33
  34 namespace ash {
  35 namespace {
  36
  37 // The duration of the drag cancel animation in millisecond.
  38 const int kCancelAnimationDuration = 250;
  39 const int kTouchCancelAnimationDuration = 20;
  40 // The frame rate of the drag cancel animation in hertz.
  41 const int kCancelAnimationFrameRate = 60;
  42
  43 // For touch initiated dragging, we scale and shift drag image by the following:
  44 static const float kTouchDragImageScale = 1.2f;
  45 static const int kTouchDragImageVerticalOffset = -25;
  46
  47 // Adjusts the drag image bounds such that the new bounds are scaled by |scale|
  48 // and translated by the |drag_image_offset| and and additional
  49 // |vertical_offset|.
  50 gfx::Rect AdjustDragImageBoundsForScaleAndOffset(
  51     const gfx::Rect& drag_image_bounds,
  52     int vertical_offset,
  53     float scale,
  54     gfx::Vector2d* drag_image_offset) {
  55   gfx::PointF final_origin = drag_image_bounds.origin();
  56   gfx::SizeF final_size = drag_image_bounds.size();
  57   final_size.Scale(scale);
  58   drag_image_offset->set_x(drag_image_offset->x() * scale);
  59   drag_image_offset->set_y(drag_image_offset->y() * scale);
  60   float total_x_offset = drag_image_offset->x();
  61   float total_y_offset = drag_image_offset->y() - vertical_offset;
  62   final_origin.Offset(-total_x_offset, -total_y_offset);
  63   return gfx::ToEnclosingRect(gfx::RectF(final_origin, final_size));
  64 }
  65
  66 void DispatchGestureEndToWindow(aura::Window* window) {
  67   if (window && window->delegate()) {
  68     ui::GestureEvent gesture_end(0,
  69                                  0,
  70                                  0,
  71                                  ui::EventTimeForNow(),
  72                                  ui::GestureEventDetails(ui::ET_GESTURE_END));
  73     window->delegate()->OnGestureEvent(&gesture_end);
  74   }
  75 }
  76 }  // namespace
  77
  78 class DragDropTrackerDelegate : public aura::WindowDelegate {
  79  public:
  80   explicit DragDropTrackerDelegate(DragDropController* controller)
  81       : drag_drop_controller_(controller) {}
  82   ~DragDropTrackerDelegate() override {}
  83
  84   // Overridden from WindowDelegate:
  85   gfx::Size GetMinimumSize() const override { return gfx::Size(); }
  86
  87   gfx::Size GetMaximumSize() const override { return gfx::Size(); }
  88
  89   void OnBoundsChanged(const gfx::Rect& old_bounds,
  90                        const gfx::Rect& new_bounds) override {}
  91   ui::TextInputClient* GetFocusedTextInputClient() override { return nullptr; }
  92   gfx::NativeCursor GetCursor(const gfx::Point& point) override {
  93     return gfx::kNullCursor;
  94   }
  95   int GetNonClientComponent(const gfx::Point& point) const override {
  96     return HTCAPTION;
  97   }
  98   bool ShouldDescendIntoChildForEventHandling(
  99       aura::Window* child,
 100       const gfx::Point& location) override {
 101     return true;
 102   }
 103   bool CanFocus() override { return true; }
 104   void OnCaptureLost() override {
 105     if (drag_drop_controller_->IsDragDropInProgress())
 106       drag_drop_controller_->DragCancel();
 107   }
 108   void OnPaint(const ui::PaintContext& context) override {}
 109   void OnDeviceScaleFactorChanged(float device_scale_factor) override {}
 110   void OnWindowDestroying(aura::Window* window) override {}
 111   void OnWindowDestroyed(aura::Window* window) override {}
 112   void OnWindowTargetVisibilityChanged(bool visible) override {}
 113   bool HasHitTestMask() const override { return true; }
 114   void GetHitTestMask(gfx::Path* mask) const override {
 115     DCHECK(mask->isEmpty());
 116   }
 117
 118  private:
 119   DragDropController* drag_drop_controller_;
 120
 121   DISALLOW_COPY_AND_ASSIGN(DragDropTrackerDelegate);
 122 };
 123
 124 ////////////////////////////////////////////////////////////////////////////////
 125 // DragDropController, public:
 126
 127 DragDropController::DragDropController()
 128     : drag_data_(NULL),
 129       drag_operation_(0),
 130       drag_window_(NULL),
 131       drag_source_window_(NULL),
 132       should_block_during_drag_drop_(true),
 133       drag_drop_window_delegate_(new DragDropTrackerDelegate(this)),
 134       current_drag_event_source_(ui::DragDropTypes::DRAG_EVENT_SOURCE_MOUSE),
 135       weak_factory_(this) {
 136   Shell::GetInstance()->PrependPreTargetHandler(this);
 137 }
 138
 139 DragDropController::~DragDropController() {
 140   Shell::GetInstance()->RemovePreTargetHandler(this);
 141   Cleanup();
 142   if (cancel_animation_)
 143     cancel_animation_->End();
 144   if (drag_image_)
 145     drag_image_.reset();
 146 }
 147
 148 int DragDropController::StartDragAndDrop(
 149     const ui::OSExchangeData& data,
 150     aura::Window* root_window,
 151     aura::Window* source_window,
 152     const gfx::Point& screen_location,
 153     int operation,
 154     ui::DragDropTypes::DragEventSource source) {
 155   if (IsDragDropInProgress())
 156     return 0;
 157
 158   const ui::OSExchangeData::Provider* provider = &data.provider();
 159   // We do not support touch drag/drop without a drag image.
 160   if (source == ui::DragDropTypes::DRAG_EVENT_SOURCE_TOUCH &&
 161       provider->GetDragImage().size().IsEmpty())
 162     return 0;
 163
 164   UMA_HISTOGRAM_ENUMERATION("Event.DragDrop.Start", source,
 165                             ui::DragDropTypes::DRAG_EVENT_SOURCE_COUNT);
 166
 167   current_drag_event_source_ = source;
 168   DragDropTracker* tracker =
 169       new DragDropTracker(root_window, drag_drop_window_delegate_.get());
 170   if (source == ui::DragDropTypes::DRAG_EVENT_SOURCE_TOUCH) {
 171     // We need to transfer the current gesture sequence and the GR's touch event
 172     // queue to the |drag_drop_tracker_|'s capture window so that when it takes
 173     // capture, it still gets a valid gesture state.
 174     ui::GestureRecognizer::Get()->TransferEventsTo(source_window,
 175         tracker->capture_window());
 176     // We also send a gesture end to the source window so it can clear state.
 177     // TODO(varunjain): Remove this whole block when gesture sequence
 178     // transferring is properly done in the GR (http://crbug.com/160558)
 179     DispatchGestureEndToWindow(source_window);
 180   }
 181   tracker->TakeCapture();
 182   drag_drop_tracker_.reset(tracker);
 183   drag_source_window_ = source_window;
 184   if (drag_source_window_)
 185     drag_source_window_->AddObserver(this);
 186   pending_long_tap_.reset();
 187
 188   drag_data_ = &data;
 189   drag_operation_ = operation;
 190
 191   float drag_image_scale = 1;
 192   int drag_image_vertical_offset = 0;
 193   if (source == ui::DragDropTypes::DRAG_EVENT_SOURCE_TOUCH) {
 194     drag_image_scale = kTouchDragImageScale;
 195     drag_image_vertical_offset = kTouchDragImageVerticalOffset;
 196   }
 197   gfx::Point start_location = screen_location;
 198   drag_image_final_bounds_for_cancel_animation_ = gfx::Rect(
 199       start_location - provider->GetDragImageOffset(),
 200       provider->GetDragImage().size());
 201   drag_image_.reset(new DragImageView(source_window->GetRootWindow(), source));
 202   drag_image_->SetImage(provider->GetDragImage());
 203   drag_image_offset_ = provider->GetDragImageOffset();
 204   gfx::Rect drag_image_bounds(start_location, drag_image_->GetPreferredSize());
 205   drag_image_bounds = AdjustDragImageBoundsForScaleAndOffset(drag_image_bounds,
 206       drag_image_vertical_offset, drag_image_scale, &drag_image_offset_);
 207   drag_image_->SetBoundsInScreen(drag_image_bounds);
 208   drag_image_->SetWidgetVisible(true);
 209   if (source == ui::DragDropTypes::DRAG_EVENT_SOURCE_TOUCH) {
 210     drag_image_->SetTouchDragOperationHintPosition(gfx::Point(
 211         drag_image_offset_.x(),
 212         drag_image_offset_.y() + drag_image_vertical_offset));
 213   }
 214
 215   drag_window_ = NULL;
 216
 217   // Ends cancel animation if it's in progress.
 218   if (cancel_animation_)
 219     cancel_animation_->End();
 220
 221   if (should_block_during_drag_drop_) {
 222     base::RunLoop run_loop;
 223     quit_closure_ = run_loop.QuitClosure();
 224     base::MessageLoopForUI* loop = base::MessageLoopForUI::current();
 225     base::MessageLoop::ScopedNestableTaskAllower allow_nested(loop);
 226     run_loop.Run();
 227   }
 228
 229   if (drag_operation_ == 0) {
 230     UMA_HISTOGRAM_ENUMERATION("Event.DragDrop.Cancel", source,
 231                               ui::DragDropTypes::DRAG_EVENT_SOURCE_COUNT);
 232   } else {
 233     UMA_HISTOGRAM_ENUMERATION("Event.DragDrop.Drop", source,
 234                               ui::DragDropTypes::DRAG_EVENT_SOURCE_COUNT);
 235   }
 236
 237   if (!cancel_animation_.get() || !cancel_animation_->is_animating() ||
 238       !pending_long_tap_.get()) {
 239     // If drag cancel animation is running, this cleanup is done when the
 240     // animation completes.
 241     if (drag_source_window_)
 242       drag_source_window_->RemoveObserver(this);
 243     drag_source_window_ = NULL;
 244   }
 245
 246   return drag_operation_;
 247 }
 248
 249 void DragDropController::DragUpdate(aura::Window* target,
 250                                     const ui::LocatedEvent& event) {
 251   int op = ui::DragDropTypes::DRAG_NONE;
 252   if (target != drag_window_) {
 253     if (drag_window_) {
 254       aura::client::DragDropDelegate* delegate =
 255           aura::client::GetDragDropDelegate(drag_window_);
 256       if (delegate)
 257         delegate->OnDragExited();
 258       if (drag_window_ != drag_source_window_)
 259         drag_window_->RemoveObserver(this);
 260     }
 261     drag_window_ = target;
 262     // We are already an observer of |drag_source_window_| so no need to add.
 263     if (drag_window_ != drag_source_window_)
 264       drag_window_->AddObserver(this);
 265     aura::client::DragDropDelegate* delegate =
 266         aura::client::GetDragDropDelegate(drag_window_);
 267     if (delegate) {
 268       ui::DropTargetEvent e(*drag_data_,
 269                             event.location(),
 270                             event.root_location(),
 271                             drag_operation_);
 272       e.set_flags(event.flags());
 273       delegate->OnDragEntered(e);
 274     }
 275   } else {
 276     aura::client::DragDropDelegate* delegate =
 277         aura::client::GetDragDropDelegate(drag_window_);
 278     if (delegate) {
 279       ui::DropTargetEvent e(*drag_data_,
 280                             event.location(),
 281                             event.root_location(),
 282                             drag_operation_);
 283       e.set_flags(event.flags());
 284       op = delegate->OnDragUpdated(e);
 285       gfx::NativeCursor cursor = ui::kCursorNoDrop;
 286       if (op & ui::DragDropTypes::DRAG_COPY)
 287         cursor = ui::kCursorCopy;
 288       else if (op & ui::DragDropTypes::DRAG_LINK)
 289         cursor = ui::kCursorAlias;
 290       else if (op & ui::DragDropTypes::DRAG_MOVE)
 291         cursor = ui::kCursorGrabbing;
 292       ash::Shell::GetInstance()->cursor_manager()->SetCursor(cursor);
 293     }
 294   }
 295
 296   DCHECK(drag_image_.get());
 297   if (drag_image_->visible()) {
 298     gfx::Point root_location_in_screen = event.root_location();
 299     ::wm::ConvertPointToScreen(target->GetRootWindow(),
 300                                &root_location_in_screen);
 301     drag_image_->SetScreenPosition(
 302         root_location_in_screen - drag_image_offset_);
 303     drag_image_->SetTouchDragOperation(op);
 304   }
 305 }
 306
 307 void DragDropController::Drop(aura::Window* target,
 308                               const ui::LocatedEvent& event) {
 309   ash::Shell::GetInstance()->cursor_manager()->SetCursor(ui::kCursorPointer);
 310
 311   // We must guarantee that a target gets a OnDragEntered before Drop. WebKit
 312   // depends on not getting a Drop without DragEnter. This behavior is
 313   // consistent with drag/drop on other platforms.
 314   if (target != drag_window_)
 315     DragUpdate(target, event);
 316   DCHECK(target == drag_window_);
 317
 318   aura::client::DragDropDelegate* delegate =
 319       aura::client::GetDragDropDelegate(target);
 320   if (delegate) {
 321     ui::DropTargetEvent e(
 322         *drag_data_, event.location(), event.root_location(), drag_operation_);
 323     e.set_flags(event.flags());
 324     drag_operation_ = delegate->OnPerformDrop(e);
 325     if (drag_operation_ == 0)
 326       StartCanceledAnimation(kCancelAnimationDuration);
 327     else
 328       drag_image_.reset();
 329   } else {
 330     drag_image_.reset();
 331   }
 332
 333   Cleanup();
 334   if (should_block_during_drag_drop_)
 335     quit_closure_.Run();
 336 }
 337
 338 void DragDropController::DragCancel() {
 339   DoDragCancel(kCancelAnimationDuration);
 340 }
 341
 342 bool DragDropController::IsDragDropInProgress() {
 343   return !!drag_drop_tracker_.get();
 344 }
 345
 346 void DragDropController::OnKeyEvent(ui::KeyEvent* event) {
 347   if (IsDragDropInProgress() && event->key_code() == ui::VKEY_ESCAPE) {
 348     DragCancel();
 349     event->StopPropagation();
 350   }
 351 }
 352
 353 void DragDropController::OnMouseEvent(ui::MouseEvent* event) {
 354   if (!IsDragDropInProgress())
 355     return;
 356
 357   // If current drag session was not started by mouse, dont process this mouse
 358   // event, but consume it so it does not interfere with current drag session.
 359   if (current_drag_event_source_ !=
 360       ui::DragDropTypes::DRAG_EVENT_SOURCE_MOUSE) {
 361     event->StopPropagation();
 362     return;
 363   }
 364
 365   aura::Window* translated_target = drag_drop_tracker_->GetTarget(*event);
 366   if (!translated_target) {
 367     DragCancel();
 368     event->StopPropagation();
 369     return;
 370   }
 371   scoped_ptr<ui::LocatedEvent> translated_event(
 372       drag_drop_tracker_->ConvertEvent(translated_target, *event));
 373   switch (translated_event->type()) {
 374     case ui::ET_MOUSE_DRAGGED:
 375       DragUpdate(translated_target, *translated_event.get());
 376       break;
 377     case ui::ET_MOUSE_RELEASED:
 378       Drop(translated_target, *translated_event.get());
 379       break;
 380     default:
 381       // We could also reach here because RootWindow may sometimes generate a
 382       // bunch of fake mouse events
 383       // (aura::RootWindow::PostMouseMoveEventAfterWindowChange).
 384       break;
 385   }
 386   event->StopPropagation();
 387 }
 388
 389 void DragDropController::OnTouchEvent(ui::TouchEvent* event) {
 390   if (!IsDragDropInProgress())
 391     return;
 392
 393   // If current drag session was not started by touch, dont process this touch
 394   // event, but consume it so it does not interfere with current drag session.
 395   if (current_drag_event_source_ != ui::DragDropTypes::DRAG_EVENT_SOURCE_TOUCH)
 396     event->StopPropagation();
 397
 398   if (event->handled())
 399     return;
 400
 401   if (event->type() == ui::ET_TOUCH_CANCELLED)
 402     DragCancel();
 403 }
 404
 405 void DragDropController::OnGestureEvent(ui::GestureEvent* event) {
 406   if (!IsDragDropInProgress())
 407     return;
 408
 409   // No one else should handle gesture events when in drag drop. Note that it is
 410   // not enough to just set ER_HANDLED because the dispatcher only stops
 411   // dispatching when the event has ER_CONSUMED. If we just set ER_HANDLED, the
 412   // event will still be dispatched to other handlers and we depend on
 413   // individual handlers' kindness to not touch events marked ER_HANDLED (not
 414   // all handlers are so kind and may cause bugs like crbug.com/236493).
 415   event->StopPropagation();
 416
 417   // If current drag session was not started by touch, dont process this event.
 418   if (current_drag_event_source_ != ui::DragDropTypes::DRAG_EVENT_SOURCE_TOUCH)
 419     return;
 420
 421   // Apply kTouchDragImageVerticalOffset to the location.
 422   ui::GestureEvent touch_offset_event(*event,
 423                                       static_cast<aura::Window*>(NULL),
 424                                       static_cast<aura::Window*>(NULL));
 425   gfx::Point touch_offset_location = touch_offset_event.location();
 426   gfx::Point touch_offset_root_location = touch_offset_event.root_location();
 427   touch_offset_location.Offset(0, kTouchDragImageVerticalOffset);
 428   touch_offset_root_location.Offset(0, kTouchDragImageVerticalOffset);
 429   touch_offset_event.set_location(touch_offset_location);
 430   touch_offset_event.set_root_location(touch_offset_root_location);
 431
 432   aura::Window* translated_target =
 433       drag_drop_tracker_->GetTarget(touch_offset_event);
 434   if (!translated_target) {
 435     DragCancel();
 436     event->SetHandled();
 437     return;
 438   }
 439   scoped_ptr<ui::LocatedEvent> translated_event(
 440       drag_drop_tracker_->ConvertEvent(translated_target, touch_offset_event));
 441
 442   switch (event->type()) {
 443     case ui::ET_GESTURE_SCROLL_UPDATE:
 444       DragUpdate(translated_target, *translated_event.get());
 445       break;
 446     case ui::ET_GESTURE_SCROLL_END:
 447     case ui::ET_SCROLL_FLING_START:
 448       Drop(translated_target, *translated_event.get());
 449       break;
 450     case ui::ET_GESTURE_LONG_TAP:
 451       // Ideally we would want to just forward this long tap event to the
 452       // |drag_source_window_|. However, webkit does not accept events while a
 453       // drag drop is still in progress. The drag drop ends only when the nested
 454       // message loop ends. Due to this stupidity, we have to defer forwarding
 455       // the long tap.
 456       pending_long_tap_.reset(
 457           new ui::GestureEvent(*event,
 458               static_cast<aura::Window*>(drag_drop_tracker_->capture_window()),
 459               static_cast<aura::Window*>(drag_source_window_)));
 460       DoDragCancel(kTouchCancelAnimationDuration);
 461       break;
 462     default:
 463       break;
 464   }
 465   event->SetHandled();
 466 }
 467
 468 void DragDropController::OnWindowDestroyed(aura::Window* window) {
 469   if (drag_window_ == window)
 470     drag_window_ = NULL;
 471   if (drag_source_window_ == window)
 472     drag_source_window_ = NULL;
 473 }
 474
 475 ////////////////////////////////////////////////////////////////////////////////
 476 // DragDropController, protected:
 477
 478 gfx::LinearAnimation* DragDropController::CreateCancelAnimation(
 479     int duration,
 480     int frame_rate,
 481     gfx::AnimationDelegate* delegate) {
 482   return new gfx::LinearAnimation(duration, frame_rate, delegate);
 483 }
 484
 485 ////////////////////////////////////////////////////////////////////////////////
 486 // DragDropController, private:
 487
 488 void DragDropController::AnimationEnded(const gfx::Animation* animation) {
 489   cancel_animation_.reset();
 490
 491   // By the time we finish animation, another drag/drop session may have
 492   // started. We do not want to destroy the drag image in that case.
 493   if (!IsDragDropInProgress())
 494     drag_image_.reset();
 495   if (pending_long_tap_) {
 496     // If not in a nested message loop, we can forward the long tap right now.
 497     if (!should_block_during_drag_drop_) {
 498       ForwardPendingLongTap();
 499     } else {
 500       // See comment about this in OnGestureEvent().
 501       base::MessageLoopForUI::current()->PostTask(
 502           FROM_HERE,
 503           base::Bind(&DragDropController::ForwardPendingLongTap,
 504                      weak_factory_.GetWeakPtr()));
 505     }
 506   }
 507 }
 508
 509 void DragDropController::DoDragCancel(int drag_cancel_animation_duration_ms) {
 510   ash::Shell::GetInstance()->cursor_manager()->SetCursor(ui::kCursorPointer);
 511
 512   // |drag_window_| can be NULL if we have just started the drag and have not
 513   // received any DragUpdates, or, if the |drag_window_| gets destroyed during
 514   // a drag/drop.
 515   aura::client::DragDropDelegate* delegate = drag_window_?
 516       aura::client::GetDragDropDelegate(drag_window_) : NULL;
 517   if (delegate)
 518     delegate->OnDragExited();
 519
 520   Cleanup();
 521   drag_operation_ = 0;
 522   StartCanceledAnimation(drag_cancel_animation_duration_ms);
 523   if (should_block_during_drag_drop_)
 524     quit_closure_.Run();
 525 }
 526
 527 void DragDropController::AnimationProgressed(const gfx::Animation* animation) {
 528   gfx::Rect current_bounds = animation->CurrentValueBetween(
 529       drag_image_initial_bounds_for_cancel_animation_,
 530       drag_image_final_bounds_for_cancel_animation_);
 531   drag_image_->SetBoundsInScreen(current_bounds);
 532 }
 533
 534 void DragDropController::AnimationCanceled(const gfx::Animation* animation) {
 535   AnimationEnded(animation);
 536 }
 537
 538 void DragDropController::StartCanceledAnimation(int animation_duration_ms) {
 539   DCHECK(drag_image_.get());
 540   drag_image_->SetTouchDragOperationHintOff();
 541   drag_image_initial_bounds_for_cancel_animation_ =
 542       drag_image_->GetBoundsInScreen();
 543   cancel_animation_.reset(CreateCancelAnimation(animation_duration_ms,
 544                                                 kCancelAnimationFrameRate,
 545                                                 this));
 546   cancel_animation_->Start();
 547 }
 548
 549 void DragDropController::ForwardPendingLongTap() {
 550   if (drag_source_window_ && drag_source_window_->delegate()) {
 551     drag_source_window_->delegate()->OnGestureEvent(pending_long_tap_.get());
 552     DispatchGestureEndToWindow(drag_source_window_);
 553   }
 554   pending_long_tap_.reset();
 555   if (drag_source_window_)
 556     drag_source_window_->RemoveObserver(this);
 557   drag_source_window_ = NULL;
 558 }
 559
 560 void DragDropController::Cleanup() {
 561   if (drag_window_)
 562     drag_window_->RemoveObserver(this);
 563   drag_window_ = NULL;
 564   drag_data_ = NULL;
 565   // Cleanup can be called again while deleting DragDropTracker, so delete
 566   // the pointer with a local variable to avoid double free.
 567   scoped_ptr<ash::DragDropTracker> holder = drag_drop_tracker_.Pass();
 568 }
 569
 570 }  // namespace ash