overview: Cancel nudge if window destroyed.

Speculative fix for the linked bug. Was unable to repro manually, but
created a test case that is plausible that has a similar stack trace.

Test: TabletModeOverviewSessionTest.DestroyWindowDuringNudge
Bug: 997335
Change-Id: Ib580740b4c059aa30e44af57e895c27b610f1650
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2225587Reviewed-by: Xiaoqian Dai <xdai@chromium.org>
Commit-Queue: Sammie Quon <sammiequon@chromium.org>
Cr-Commit-Position: refs/heads/master@{#775261}

ash/wm/overview/overview_grid.cc

@@ -370,6 +370,8 @@ OverviewGrid::OverviewGrid(aura::Window* root_window,
 OverviewGrid::~OverviewGrid() = default;
 
 void OverviewGrid::Shutdown() {
+  EndNudge();
+
   SplitViewController::Get(root_window_)->RemoveObserver(this);
   ScreenRotationAnimator::GetForRootWindow(root_window_)->RemoveObserver(this);
   Shell::Get()->wallpaper_controller()->RemoveObserver(this);
@@ -591,6 +593,8 @@ void OverviewGrid::AddItemInMruOrder(aura::Window* window,
 void OverviewGrid::RemoveItem(OverviewItem* overview_item,
                               bool item_destroying,
                               bool reposition) {
+  EndNudge();
+
   // Use reverse iterator to be efficient when removing all.
   auto iter = std::find_if(window_list_.rbegin(), window_list_.rend(),
                            base::MatchesUniquePtr(overview_item));

ash/wm/overview/overview_session_unittest.cc

@@ -3776,6 +3776,31 @@ TEST_P(TabletModeOverviewSessionTest, NoNudgingWhenLastItemOnPreviousRowDrops) {
   EXPECT_EQ(item_bounds[4], items[4]->target_bounds());
 }
 
+// Tests that there is no crash when destroying a window during a nudge drag.
+// Regression test for https://crbug.com/997335.
+TEST_P(TabletModeOverviewSessionTest, DestroyWindowDuringNudge) {
+  std::unique_ptr<aura::Window> window1 = CreateTestWindow();
+  std::unique_ptr<aura::Window> window2 = CreateTestWindow();
+  std::unique_ptr<aura::Window> window3 = CreateTestWindow();
+
+  ToggleOverview();
+  ASSERT_TRUE(overview_controller()->InOverviewSession());
+
+  OverviewItem* item = GetOverviewItemForWindow(window1.get());
+  const gfx::PointF item_center = item->target_bounds().CenterPoint();
+
+  // Drag |item1| vertically to start nudging.
+  overview_session()->InitiateDrag(item, item_center,
+                                   /*is_touch_dragging=*/true);
+  overview_session()->Drag(item, item_center + gfx::Vector2dF(0, 160));
+
+  // Destroy |window2| and |window3|,then keep dragging. There should be no
+  // crash.
+  window2.reset();
+  window3.reset();
+  overview_session()->Drag(item, item_center + gfx::Vector2dF(0, 260));
+}
+
 TEST_P(TabletModeOverviewSessionTest, MultiTouch) {
   const gfx::Rect bounds(400, 400);
   std::unique_ptr<aura::Window> window1(CreateTestWindow(bounds));