split view: Record overview animation histogram for snapping two windows

Overview exit animation histograms shall include when overview ends
because you drag two windows from overview and snap on opposite sides.

Test: All/SplitViewOverviewSessionInClamshellTest.BothSnappedOverviewExitAnimationHistogramTest/?
Change-Id: I5a1e7d11a4e6d4e3aff49c32e489b9042aa5cf0e
Fixed: 1124786
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2401941Reviewed-by: Xiaoqian Dai <xdai@chromium.org>
Commit-Queue: Avery Musbach <amusbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#806377}

ash/wm/splitview/split_view_controller.cc

@@ -1366,11 +1366,11 @@ void SplitViewController::OnOverviewModeEnding(
   if (state_ == State::kBothSnapped)
     overview_session->SetWindowListNotAnimatedWhenExiting(root_window_);
 
-  // If clamshell split view mode is active, end it and bail out.
-  if (split_view_type_ == SplitViewType::kClamshellType) {
-    EndSplitView();
+  // If clamshell split view mode is active, bail out. |OnOverviewModeEnded|
+  // will end split view. We do not end split view here, because that would mess
+  // up histograms of overview exit animation smoothness.
+  if (split_view_type_ == SplitViewType::kClamshellType)
     return;
-  }
 
   // Tablet split view mode is active. If it still only has one snapped window,
   // snap the first snappable window in the overview grid on the other side.
@@ -1406,6 +1406,12 @@ void SplitViewController::OnOverviewModeEnding(
   ShowAppCannotSnapToast();
 }
 
+void SplitViewController::OnOverviewModeEnded() {
+  DCHECK(InSplitViewMode());
+  if (split_view_type_ == SplitViewType::kClamshellType)
+    EndSplitView();
+}
+
 void SplitViewController::OnDisplayRemoved(
     const display::Display& old_display) {
   // Display removal always triggers a window activation which ends overview,

ash/wm/splitview/split_view_controller.h

@@ -247,6 +247,7 @@ class ASH_EXPORT SplitViewController : public aura::WindowObserver,
   // OverviewObserver:
   void OnOverviewModeStarting() override;
   void OnOverviewModeEnding(OverviewSession* overview_session) override;
+  void OnOverviewModeEnded() override;
 
   // display::DisplayObserver:
   void OnDisplayRemoved(const display::Display& old_display) override;