overview: Re-enable two tests and fix a DCHECK.

DCHECK in OverviewGrid::AddDropTargetForDraggingFromOverview can be hit
if long-press two items at the same time with different fingers. One
test was flaky on mash.

Test: none
Bug: 941048
Change-Id: I6a1f1884ecec53714d915cf4a671c621c18d7793
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1776592
Commit-Queue: Sammie Quon <sammiequon@chromium.org>
Reviewed-by: Scott Violet <sky@chromium.org>
Cr-Commit-Position: refs/heads/master@{#692144}

ash/wm/overview/overview_item.cc

@@ -1087,6 +1087,9 @@ void OverviewItem::HandleDragEvent(const gfx::PointF& location_in_screen) {
 }
 
 void OverviewItem::HandleLongPressEvent(const gfx::PointF& location_in_screen) {
+  if (!IsDragItem())
+    return;
+
   if (ShouldAllowSplitView() || desks_util::ShouldDesksBarBeCreated())
     overview_session_->StartNormalDragMode(location_in_screen);
 }

ash/wm/overview/overview_session_unittest.cc

@@ -2369,9 +2369,7 @@ class OverviewSessionRoundedCornerTest : public OverviewSessionTest {
 
 // Test that the mask that is applied to add rounded corners in overview mode
 // is removed during animations.
-// TODO(crbug.com/941048): this test leaks WindowMirrorView, which causes
-// problems. Fix leak and then reenable.
-TEST_F(OverviewSessionRoundedCornerTest, DISABLED_RoundedEdgeMaskVisibility) {
+TEST_F(OverviewSessionRoundedCornerTest, RoundedEdgeMaskVisibility) {
   std::unique_ptr<aura::Window> window1(CreateTestWindow());
   std::unique_ptr<aura::Window> window2(CreateTestWindow());
 
@@ -2557,14 +2555,12 @@ TEST_F(OverviewSessionTest, ShadowBounds) {
 }
 
 // Verify that attempting to drag with a secondary finger works as expected.
-// Disabled due to flakiness: crbug.com/834708
-TEST_F(OverviewSessionTest, DISABLED_DraggingWithTwoFingers) {
+TEST_F(OverviewSessionTest, DraggingWithTwoFingers) {
   std::unique_ptr<aura::Window> window1(CreateTestWindow());
   std::unique_ptr<aura::Window> window2(CreateTestWindow());
 
   EnterTabletMode();
   ToggleOverview();
-  base::RunLoop().RunUntilIdle();
   OverviewItem* item1 = GetOverviewItemForWindow(window1.get());
   OverviewItem* item2 = GetOverviewItemForWindow(window2.get());
 
@@ -2616,7 +2612,6 @@ TEST_F(OverviewSessionTest, DISABLED_DraggingWithTwoFingers) {
   last_center_point = item1->target_bounds().CenterPoint();
   generator->ReleaseTouchId(kTouchId2);
   generator->PressTouchId(kTouchId2);
-  dispatch_long_press();
   generator->MoveTouchIdBy(kTouchId2, 40, 40);
   EXPECT_NE(last_center_point, item1->target_bounds().CenterPoint());
   EXPECT_EQ(original_bounds2.CenterPoint(),