Revert of Remove CompositorObserver::OnCompositingEnded()

ui/snapshot/snapshot_aura_unittest.cc

 // Copyright (c) 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ui/snapshot/snapshot.h"
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include "base/bind.h"
@@ skipping 108 matching lines @@
     testing::Test::TearDown();
   }
 
  protected:
   aura::Window* test_window() { return test_window_.get(); }
   aura::Window* root_window() { return helper_->root_window(); }
   aura::TestScreen* test_screen() { return helper_->test_screen(); }
 
   void WaitForDraw() {
     helper_->host()->compositor()->ScheduleDraw();
-    ui::DrawWaiterForTest::WaitForCompositingStarted(
+    ui::DrawWaiterForTest::WaitForCompositingEnded(
         helper_->host()->compositor());
   }
 
   void SetupTestWindow(const gfx::Rect& window_bounds) {
     delegate_.reset(new TestPaintingWindowDelegate(window_bounds.size()));
     test_window_.reset(aura::test::CreateTestWindowWithDelegate(
         delegate_.get(), 0, window_bounds, root_window()));
   }
 
   gfx::Image GrabSnapshotForTestWindow() {
@@ skipping 146 matching lines @@
   gfx::SizeF snapshot_size(test_bounds.size());
   snapshot_size.Scale(2.0f / kUIScale);
 
   gfx::Image snapshot = GrabSnapshotForTestWindow();
   EXPECT_EQ(gfx::ToRoundedSize(snapshot_size).ToString(),
             snapshot.Size().ToString());
   EXPECT_EQ(0u, GetFailedPixelsCountWithScaleFactor(snapshot, 2 / kUIScale));
 }
 
 }  // namespace ui