base: Cleanup class/struct forward declarations

cc/test/fake_raster_source.h

 // Copyright 2015 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 CC_TEST_FAKE_RASTER_SOURCE_H_
 #define CC_TEST_FAKE_RASTER_SOURCE_H_
 
 #include "base/memory/ref_counted.h"
 #include "cc/playback/raster_source.h"
 #include "ui/gfx/geometry/rect.h"
 #include "ui/gfx/geometry/size.h"
 
 class SkCanvas;
 
+namespace base {
+class WaitableEvent;
+}
+
 namespace cc {
 
 class RecordingSource;
 
 class FakeRasterSource : public RasterSource {
  public:
   static scoped_refptr<FakeRasterSource> CreateInfiniteFilled();
   static scoped_refptr<FakeRasterSource> CreateFilled(const gfx::Size& size);
   static scoped_refptr<FakeRasterSource> CreateFilledLCD(const gfx::Size& size);
   static scoped_refptr<FakeRasterSource> CreateFilledSolidColor(
@@ skipping 20 matching lines @@
                    base::WaitableEvent* playback_allowed_event);
   ~FakeRasterSource() override;
 
  private:
   base::WaitableEvent* playback_allowed_event_;
 };
 
 }  // namespace cc
 
 #endif  // CC_TEST_FAKE_RASTER_SOURCE_H_