Prefer to forward-declare GraphicsContext in headers.

Source/platform/graphics/BitmapImage.cpp

 /*
  * Copyright (C) 2006 Samuel Weinig (sam.weinig@gmail.com)
  * Copyright (C) 2004, 2005, 2006, 2008 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
@@ skipping 10 matching lines @@
  * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
  * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
 #include "config.h"
 #include "platform/graphics/BitmapImage.h"
 
 #include "platform/Timer.h"
+#include "platform/TraceEvent.h"
 #include "platform/geometry/FloatRect.h"
 #include "platform/graphics/GraphicsContextStateSaver.h"
 #include "platform/graphics/ImageObserver.h"
 #include "platform/graphics/skia/NativeImageSkia.h"
 #include "platform/graphics/skia/SkiaUtils.h"
 #include "wtf/CurrentTime.h"
 #include "wtf/PassRefPtr.h"
 #include "wtf/Vector.h"
 #include "wtf/text/WTFString.h"
 
@@ skipping 582 matching lines @@
     }
     return m_isSolidColor && !m_currentFrame;
 }
 
 Color BitmapImage::solidColor() const
 {
     return m_solidColor;
 }
 
 }