Reland "overview: Fix how multi touch works for overview drag."

This is a reland of c6e9dffe

TBR=oshima@chromium.org

Original change's description:
> overview: Fix how multi touch works for overview drag.
>
> Using two fingers was not restricted which brought a bunch of other bugs.
> Only allow one item to be dragged at a time. Still allows switching of
> fingers midway, so we just check the item which requests drag events is
> the same as the current drag item, instead of checking the gesture
> finger id.
>
> Test: ash_unittests WindowSelectorTest.DraggingWithTwoFingers
> Bug: 827435
> Change-Id: I2c897b1b3c483b5df7a98a658f575a6ebd706acd
> Reviewed-on: https://chromium-review.googlesource.com/988294
> Commit-Queue: Sammie Quon <sammiequon@chromium.org>
> Reviewed-by: Mitsuru Oshima <oshima@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#547932}

Bug: 827435
Change-Id: I1cda10e4712f79e458f5b977779809a1ed8255d5
Reviewed-on: https://chromium-review.googlesource.com/996052Reviewed-by: Sammie Quon <sammiequon@chromium.org>
Commit-Queue: Sammie Quon <sammiequon@chromium.org>
Cr-Commit-Position: refs/heads/master@{#548097}

ash/wm/overview/overview_window_drag_controller.cc

@@ -90,6 +90,7 @@ void OverviewWindowDragController::CompleteDrag(
       SnapWindow(snap_position_);
     }
   }
+  item_ = nullptr;
 }
 
 void OverviewWindowDragController::ActivateDraggedWindow() {
@@ -117,6 +118,9 @@ void OverviewWindowDragController::ResetGesture() {
   window_selector_->PositionWindows(/*animate=*/true);
   window_selector_->SetSplitViewDragIndicatorsIndicatorState(
       IndicatorState::kNone, gfx::Point());
+  // This function gets called on long press, which bypasses CompleteDrag but
+  // stops dragging as well, so reset |item_|.
+  item_ = nullptr;
 }
 
 void OverviewWindowDragController::ResetWindowSelector() {

ash/wm/overview/window_selector_item.cc

@@ -963,31 +963,52 @@ float WindowSelectorItem::GetItemScale(const gfx::Size& size) {
 
 void WindowSelectorItem::HandlePressEvent(
     const gfx::Point& location_in_screen) {
+  // We allow switching finger while dragging, but do not allow dragging two or more items.
+  if (window_selector_->window_drag_controller() &&
+      window_selector_->window_drag_controller()->item()) {
+    return;
+  }
+
   StartDrag();
   window_selector_->InitiateDrag(this, location_in_screen);
 }
 
 void WindowSelectorItem::HandleReleaseEvent(
     const gfx::Point& location_in_screen) {
+  if (!IsDragItem())
+    return;
+
   EndDrag();
   window_selector_->CompleteDrag(this, location_in_screen);
 }
 
 void WindowSelectorItem::HandleDragEvent(const gfx::Point& location_in_screen) {
+  if (!IsDragItem())
+    return;
+
   window_selector_->Drag(this, location_in_screen);
 }
 
 void WindowSelectorItem::ActivateDraggedWindow() {
-  DCHECK_EQ(this, window_selector_->window_drag_controller()->item());
+  if (!IsDragItem())
+    return;
+
   window_selector_->ActivateDraggedWindow();
 }
 
 void WindowSelectorItem::ResetDraggedWindowGesture() {
   OnSelectorItemDragEnded();
-  DCHECK_EQ(this, window_selector_->window_drag_controller()->item());
+  if (!IsDragItem())
+    return;
+
   window_selector_->ResetDraggedWindowGesture();
 }
 
+bool WindowSelectorItem::IsDragItem() {
+  return window_selector_->window_drag_controller() &&
+         window_selector_->window_drag_controller()->item() == this;
+}
+
 void WindowSelectorItem::SetShadowBounds(
     base::Optional<gfx::Rect> bounds_in_screen) {
   if (!IsNewOverviewUi())

ash/wm/overview/window_selector_item.h

@@ -185,6 +185,9 @@ class ASH_EXPORT WindowSelectorItem : public views::ButtonListener,
   void ActivateDraggedWindow();
   void ResetDraggedWindowGesture();
 
+  // Checks if this item is current being dragged.
+  bool IsDragItem();
+
   // Sets the bounds of the window shadow. If |bounds_in_screen| is nullopt,
   // the shadow is hidden.
   void SetShadowBounds(base::Optional<gfx::Rect> bounds_in_screen);

ash/wm/overview/window_selector_unittest.cc

@@ -2907,6 +2907,64 @@ TEST_F(WindowSelectorTest, ShadowBounds) {
   ToggleOverview();
 }
 
+// Verify that attempting to drag with a secondary finger works as expected.
+TEST_F(WindowSelectorTest, DraggingWithTwoFingers) {
+  std::unique_ptr<aura::Window> window1 = CreateTestWindow();
+  std::unique_ptr<aura::Window> window2 = CreateTestWindow();
+
+  // Dragging is only allowed in tablet mode.
+  RunAllPendingInMessageLoop();
+  Shell::Get()->tablet_mode_controller()->EnableTabletModeWindowManager(true);
+
+  ToggleOverview();
+  RunAllPendingInMessageLoop();
+  WindowSelectorItem* item1 = GetWindowItemForWindow(0, window1.get());
+  WindowSelectorItem* item2 = GetWindowItemForWindow(0, window2.get());
+
+  const gfx::Rect original_bounds1 = item1->target_bounds();
+  const gfx::Rect original_bounds2 = item2->target_bounds();
+
+  constexpr int kTouchId1 = 1;
+  constexpr int kTouchId2 = 2;
+
+  // Verify that the bounds of the tapped window expand when touched.
+  ui::test::EventGenerator& generator = GetEventGenerator();
+  generator.set_current_location(original_bounds1.CenterPoint());
+  generator.PressTouchId(kTouchId1);
+  RunAllPendingInMessageLoop();
+  EXPECT_GT(item1->target_bounds().width(), original_bounds1.width());
+  EXPECT_GT(item1->target_bounds().height(), original_bounds1.height());
+
+  // Verify that attempting to touch the second window with a second finger does
+  // nothing to the second window. The first window remains the window to be
+  // dragged.
+  generator.set_current_location(original_bounds2.CenterPoint());
+  generator.PressTouchId(kTouchId2);
+  RunAllPendingInMessageLoop();
+  EXPECT_GT(item1->target_bounds().width(), original_bounds1.width());
+  EXPECT_GT(item1->target_bounds().height(), original_bounds1.height());
+  EXPECT_EQ(item2->target_bounds(), original_bounds2);
+
+  // Verify the first window moves on drag.
+  gfx::Point last_center_point = item1->target_bounds().CenterPoint();
+  generator.MoveTouchIdBy(kTouchId1, 40, 40);
+  RunAllPendingInMessageLoop();
+  EXPECT_NE(last_center_point, item1->target_bounds().CenterPoint());
+  EXPECT_EQ(original_bounds2.CenterPoint(),
+            item2->target_bounds().CenterPoint());
+
+  // Verify the first window moves on drag, even if we switch to a second
+  // finger.
+  last_center_point = item1->target_bounds().CenterPoint();
+  generator.ReleaseTouchId(kTouchId2);
+  generator.PressTouchId(kTouchId2);
+  generator.MoveTouchIdBy(kTouchId2, 40, 40);
+  RunAllPendingInMessageLoop();
+  EXPECT_NE(last_center_point, item1->target_bounds().CenterPoint());
+  EXPECT_EQ(original_bounds2.CenterPoint(),
+            item2->target_bounds().CenterPoint());
+}
+
 class SplitViewWindowSelectorTest : public WindowSelectorTest {
  public:
   SplitViewWindowSelectorTest() = default;