Fix app list duplication on drag.

This CL fixes a bug where drop targets were not being calculated correctly
which led to duplication on reparents.

BUG=415530
TEST=Drag an app from inside a folder onto the page switcher. The app
should disappear from the folder and appear in the root grid.

Review URL: https://codereview.chromium.org/583263004

Cr-Commit-Position: refs/heads/master@{#296125}

ui/app_list/views/app_list_main_view_unittest.cc

@@ -264,12 +264,9 @@ TEST_F(AppListMainViewTest, DragLastItemFromFolderAndDropAtLastSlot) {
   drop_target_tile.Offset(first_slot_tile.width() * 2, 0);
   gfx::Point point = drop_target_tile.CenterPoint();
   SimulateUpdateDrag(FolderGridView(), AppsGridView::MOUSE, dragged, point);
-  SimulateUpdateDrag(FolderGridView(), AppsGridView::MOUSE, dragged, point);
-  base::RunLoop().RunUntilIdle();
 
   // Drop it.
   FolderGridView()->EndDrag(false);
-  base::RunLoop().RunUntilIdle();
 
   // Folder icon view should be gone and there is only one item view.
   EXPECT_EQ(1, RootViewModel()->view_size());
@@ -286,6 +283,35 @@ TEST_F(AppListMainViewTest, DragLastItemFromFolderAndDropAtLastSlot) {
             delegate_->GetTestModel()->FindFolderItem("single_item_folder"));
 }
 
+// Tests dragging an item out of a single item folder and dropping it onto the
+// page switcher. Regression test for http://crbug.com/415530/.
+TEST_F(AppListMainViewTest, DragReparentItemOntoPageSwitcher) {
+  AppListItemView* folder_item_view = CreateAndOpenSingleItemFolder();
+  const gfx::Rect first_slot_tile = folder_item_view->bounds();
+
+  delegate_->GetTestModel()->PopulateApps(20);
+
+  EXPECT_EQ(1, FolderViewModel()->view_size());
+  EXPECT_EQ(21, RootViewModel()->view_size());
+
+  AppListItemView* dragged = StartDragForReparent(0);
+
+  gfx::Rect main_view_bounds = main_view_->bounds();
+  // Drag the reparent item to the page switcher.
+  gfx::Point point =
+      gfx::Point(main_view_bounds.width() / 2,
+                 main_view_bounds.bottom() - first_slot_tile.height());
+  SimulateUpdateDrag(FolderGridView(), AppsGridView::MOUSE, dragged, point);
+
+  // Drop it.
+  FolderGridView()->EndDrag(false);
+
+  // The folder should be destroyed.
+  EXPECT_EQ(21, RootViewModel()->view_size());
+  EXPECT_EQ(NULL,
+            delegate_->GetTestModel()->FindFolderItem("single_item_folder"));
+}
+
 // Test that an interrupted drag while reparenting an item from a folder, when
 // canceled via the root grid, correctly forwards the cancelation to the drag
 // ocurring from the folder.

ui/app_list/views/apps_grid_view.cc

@@ -1401,6 +1401,7 @@ bool AppsGridView::CalculateFolderDropTarget(const gfx::Point& point,
       !IsFolderItem(drag_view_->item()) &&
       CanDropIntoTarget(nearest_tile_index)) {
     *drop_target = nearest_tile_index;
+    DCHECK(IsValidIndex(*drop_target));
     return true;
   }
 
@@ -1437,6 +1438,7 @@ void AppsGridView::CalculateReorderDropTarget(const gfx::Point& point,
   *drop_target =
       std::min(Index(pagination_model_.selected_page(), row * cols_ + col),
                GetLastViewIndex());
+  DCHECK(IsValidIndex(*drop_target));
 }
 
 void AppsGridView::OnReorderTimer() {
@@ -1551,6 +1553,8 @@ void AppsGridView::EndDragFromReparentItemInRootLevel(
     } else if (drop_attempt_ == DROP_FOR_FOLDER &&
                IsValidIndex(folder_drop_target_)) {
       ReparentItemToAnotherFolder(drag_view_, folder_drop_target_);
+    } else {
+      NOTREACHED();
     }
     SetViewHidden(drag_view_, false /* show */, true /* no animate */);
   }
@@ -2096,9 +2100,10 @@ AppsGridView::Index AppsGridView::GetNearestTileIndexForPoint(
   gfx::Rect bounds = GetContentsBounds();
   gfx::Size total_tile_size = GetTotalTileSize();
   int col = ClampToRange(
-      (point.x() - bounds.x()) / total_tile_size.width(), 0, cols_);
-  int row = ClampToRange(
-      (point.y() - bounds.y()) / total_tile_size.height(), 0, rows_per_page_);
+      (point.x() - bounds.x()) / total_tile_size.width(), 0, cols_ - 1);
+  int row = ClampToRange((point.y() - bounds.y()) / total_tile_size.height(),
+                         0,
+                         rows_per_page_ - 1);
   return Index(pagination_model_.selected_page(), row * cols_ + col);
 }