Revert of Remove CompositorObserver::OnCompositingEnded()

ui/compositor/test/draw_waiter_for_test.h

Index: ui/compositor/test/draw_waiter_for_test.h
diff --git a/ui/compositor/test/draw_waiter_for_test.h b/ui/compositor/test/draw_waiter_for_test.h
index 173bed91bc2522bd6dd5342bf9432e617f98bb57..f60657cf18d8e9221cd0babc920744ac089c5cdd 100644
--- a/ui/compositor/test/draw_waiter_for_test.h
+++ b/ui/compositor/test/draw_waiter_for_test.h
@@ -25,6 +25,9 @@ class DrawWaiterForTest : public CompositorObserver {
   // not to draw.
   static void WaitForCompositingStarted(Compositor* compositor);
 
+  // Waits for a swap to be completed from the compositor.
+  static void WaitForCompositingEnded(Compositor* compositor);
+
   // Waits for a commit instead of a draw.
   static void WaitForCommit(Compositor* compositor);
 
@@ -32,6 +35,7 @@ class DrawWaiterForTest : public CompositorObserver {
   enum WaitEvent {
     WAIT_FOR_COMMIT,
     WAIT_FOR_COMPOSITING_STARTED,
+    WAIT_FOR_COMPOSITING_ENDED,
   };
   DrawWaiterForTest(WaitEvent wait_event);
   ~DrawWaiterForTest() override;
@@ -42,6 +46,7 @@ class DrawWaiterForTest : public CompositorObserver {
   void OnCompositingDidCommit(Compositor* compositor) override;
   void OnCompositingStarted(Compositor* compositor,
                             base::TimeTicks start_time) override;
+  void OnCompositingEnded(Compositor* compositor) override;
   void OnCompositingLockStateChanged(Compositor* compositor) override;
   void OnCompositingShuttingDown(Compositor* compositor) override;