overview gesture: No animation when drop window back to maximize.

Skips the reposition if the window is not dropped into overview on
drag end.

Test: added test, manual
Change-Id: I80635aa657e8a2017b72b06992a1f98181754bed
Fixed: 1049206
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2496192
Commit-Queue: Sammie Quon <sammiequon@chromium.org>
Reviewed-by: Xiaoqian Dai <xdai@chromium.org>
Cr-Commit-Position: refs/heads/master@{#823345}

ash/home_screen/drag_window_from_shelf_controller.cc

@@ -397,9 +397,17 @@ void DragWindowFromShelfController::OnDragEnded(
 
     OverviewSession* overview_session = overview_controller->overview_session();
     overview_session->ResetSplitViewDragIndicatorsWindowDraggingStates();
+
+    // No need to reposition overview windows if we are not dropping the dragged
+    // window into overview. Overview will either be exited or unchanged, and
+    // the extra movement from existing window will just add unnecessary
+    // movement which will also slow down our dragged window animation.
+    if (!should_drop_window_in_overview)
+      overview_session->SuspendReposition();
     overview_session->OnWindowDragEnded(
         window_, location_in_screen, should_drop_window_in_overview,
         /*snap=*/snap_position != SplitViewController::NONE);
+    overview_session->ResumeReposition();
   }
 
   SplitViewController* split_view_controller =

ash/home_screen/drag_window_from_shelf_controller_unittest.cc

@@ -1150,6 +1150,45 @@ TEST_F(DragWindowFromShelfControllerTest, DropsIntoOverviewAtCorrectPosition) {
                     parent));
 }
 
+// Test that when the dragged window is returned to maximized state, the
+// overview grid does not animate as it can be jarring and use up unneeded
+// resources. Regression test for http://crbug.com/1049206.
+TEST_F(DragWindowFromShelfControllerTest, NoAnimationWhenReturnToMaximize) {
+  std::unique_ptr<aura::Window> window1 = CreateTestWindow();
+  std::unique_ptr<aura::Window> window2 = CreateTestWindow();
+
+  // Drag |window1| so that overview is shown.
+  const gfx::Point shelf_centerpoint =
+      Shelf::ForWindow(Shell::GetPrimaryRootWindow())
+          ->GetIdealBounds()
+          .CenterPoint();
+  StartDrag(window1.get(), shelf_centerpoint);
+  Drag(gfx::Point(200, 200), 1.f, 1.f);
+  DragWindowFromShelfControllerTestApi().WaitUntilOverviewIsShown(
+      window_drag_controller());
+
+  // Get the bounds and transform of the item associated with |item2|.
+  OverviewController* overview_controller = Shell::Get()->overview_controller();
+  ASSERT_TRUE(overview_controller->InOverviewSession());
+  OverviewItem* item = GetOverviewItemForWindow(window2.get());
+  ASSERT_TRUE(item);
+  aura::Window* item_window = item->item_widget()->GetNativeWindow();
+  const gfx::Rect pre_exit_bounds = item_window->bounds();
+  const gfx::Transform pre_exit_transform = item_window->transform();
+
+  // Drag back to the shelf, |window2|'s overview item should not move.
+  ui::ScopedAnimationDurationScaleMode non_zero_duration_mode(
+      ui::ScopedAnimationDurationScaleMode::NON_ZERO_DURATION);
+  EndDrag(shelf_centerpoint, base::nullopt);
+  EXPECT_EQ(pre_exit_bounds, item_window->bounds());
+  EXPECT_EQ(pre_exit_transform, item_window->layer()->GetTargetTransform());
+
+  // Tests that the end drag actually exited and remaximized |window1|.
+  ShellTestApi().WaitForOverviewAnimationState(
+      OverviewAnimationState::kExitAnimationComplete);
+  EXPECT_TRUE(WindowState::Get(window1.get())->IsMaximized());
+}
+
 // Tests that when dragging a snapped window is cancelled, the window
 // still keep at the original snap position.
 TEST_F(DragWindowFromShelfControllerTest,