Fix app list DCHECKs getting hit when model updates occur during dragging

ui/app_list/views/apps_grid_view.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ui/app_list/views/apps_grid_view.h"
 
 #include <algorithm>
 #include <set>
 #include <string>
 
@@ skipping 538 matching lines @@
   // we'll enter the synchronous drag.
   // NOTE we don't Run() the drag here because that causes animations not to
   // update for some reason.
   synchronous_drag_->set_shortcut_path(path);
   DCHECK(synchronous_drag_->CanRun());
 }
 #endif
 
 bool AppsGridView::UpdateDragFromItem(Pointer pointer,
                                       const ui::LocatedEvent& event) {
-  DCHECK(drag_view_);
+  if (!drag_view_)
+    return false;  // Drag canceled.
 
   gfx::Point drag_point_in_grid_view;
   ExtractDragLocation(event, &drag_point_in_grid_view);
   UpdateDrag(pointer, drag_point_in_grid_view);
   if (!dragging())
     return false;
 
   // If a drag and drop host is provided, see if the drag operation needs to be
   // forwarded.
   gfx::Point location_in_screen = drag_point_in_grid_view;
   views::View::ConvertPointToScreen(this, &location_in_screen);
   DispatchDragEventToDragAndDropHost(location_in_screen);
   if (drag_and_drop_host_)
     drag_and_drop_host_->UpdateDragIconProxy(location_in_screen);
   return true;
 }
 
 void AppsGridView::UpdateDrag(Pointer pointer, const gfx::Point& point) {
   if (folder_delegate_)
     UpdateDragStateInsideFolder(pointer, point);
 
-  // EndDrag was called before if |drag_view_| is NULL.
   if (!drag_view_)
-    return;
+    return;  // Drag canceled.
 
   if (RunSynchronousDrag())
     return;
 
   gfx::Vector2d drag_vector(point - drag_start_grid_view_);
   if (!dragging() && ExceededDragThreshold(drag_vector)) {
     drag_pointer_ = pointer;
     // Move the view to the front so that it appears on top of other views.
     ReorderChildView(drag_view_, -1);
     bounds_animator_.StopAnimatingView(drag_view_);
@@ skipping 73 matching lines @@
   } else {
     if (IsDraggingForReparentInHiddenGridView()) {
       // Forward the EndDrag event to the root level grid view.
       folder_delegate_->DispatchEndDragEventForReparent(
           false /* events_forwarded_to_drag_drop_host */,
           cancel /* cancel_drag */);
       EndDragForReparentInHiddenFolderGridView();
       return;
     }
 
+    if (IsDraggingForReparentInRootLevelGridView()) {
+      // An EndDrag can be received during a reparent via a model change. This
+      // is always a cancel and needs to be forwarded to the folder.
+      DCHECK(cancel);
+      delegate_->CancelDragInActiveFolder();
+      return;
+    }
+
     if (!cancel && dragging()) {
       // Regular drag ending path, ie, not for reparenting.
       CalculateDropTarget(last_drag_point_, true);
       if (IsValidIndex(drop_target_)) {
         if (!EnableFolderDragDropUI()) {
             MoveItemInModel(drag_view_, drop_target_);
         } else {
           if (drop_attempt_ == DROP_FOR_REORDER)
             MoveItemInModel(drag_view_, drop_target_);
           else if (drop_attempt_ == DROP_FOR_FOLDER)
@@ skipping 103 matching lines @@
   drag_start_grid_view_ = drag_point;
 
   drag_view_start_ = gfx::Point(drag_view_->x(), drag_view_->y());
 
   // Set the flag in root level grid view.
   dragging_for_reparent_item_ = true;
 }
 
 void AppsGridView::UpdateDragFromReparentItem(Pointer pointer,
                                               const gfx::Point& drag_point) {
+  // Note that if a cancel ocurrs while reparenting, the |drag_view_| in both
+  // root and folder grid views is cleared, so the check in UpdateDragFromItem()
+  // for |drag_view_| being NULL (in the folder grid) is sufficient.
   DCHECK(drag_view_);
   DCHECK(IsDraggingForReparentInRootLevelGridView());
 
   UpdateDrag(pointer, drag_point);
 }
 
 bool AppsGridView::IsDraggedView(const views::View* view) const {
   return drag_view_ == view;
 }
 
@@ skipping 1354 matching lines @@
 void AppsGridView::SetAsFolderDroppingTarget(const Index& target_index,
                                              bool is_target_folder) {
   AppListItemView* target_view =
       static_cast<AppListItemView*>(
           GetViewAtSlotOnCurrentPage(target_index.slot));
   if (target_view)
     target_view->SetAsAttemptedFolderTarget(is_target_folder);
 }
 
 }  // namespace app_list