[Aura] Support always-on-top top level window.

ui/aura/test/aura_test_base.h

 // Copyright (c) 2011 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.
 
 #ifndef UI_AURA_TEST_AURA_TEST_BASE_H_
 #define UI_AURA_TEST_AURA_TEST_BASE_H_
 #pragma once
 
 #include "base/compiler_specific.h"
 #include "base/basictypes.h"
@@ skipping 10 matching lines @@
  public:
   AuraTestBase();
   virtual ~AuraTestBase();
 
   TestStackingClient* GetTestStackingClient();
 
   // testing::Test:
   virtual void SetUp() OVERRIDE;
   virtual void TearDown() OVERRIDE;
 
+ protected:
+  // Flushes message loop.
+  void RunAllPendingInMessageLoop();
+
  private:
   MessageLoopForUI message_loop_;
   bool setup_called_;
   bool teardown_called_;
 
   DISALLOW_COPY_AND_ASSIGN(AuraTestBase);
 };
 
 }  // namespace test
 }  // namespace aura
 
 #endif  // UI_AURA_TEST_AURA_TEST_BASE_H_