Prefer to forward-declare GraphicsContext in headers.

Source/platform/graphics/GraphicsContext.h

 /*
  * Copyright (C) 2003, 2006, 2007, 2008, 2009 Apple Inc. All rights reserved.
  * Copyright (C) 2008-2009 Torch Mobile, Inc.
  * Copyright (C) 2013 Google 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.
@@ skipping 11 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.
  */
 
 #ifndef GraphicsContext_h
 #define GraphicsContext_h
 
 #include "platform/PlatformExport.h"
-#include "platform/TraceEvent.h"
 #include "platform/fonts/Font.h"
 #include "platform/geometry/FloatRect.h"
 #include "platform/graphics/DashArray.h"
 #include "platform/graphics/DrawLooperBuilder.h"
 #include "platform/graphics/ImageBufferSurface.h"
 #include "platform/graphics/ImageOrientation.h"
 #include "platform/graphics/GraphicsContextAnnotation.h"
 #include "platform/graphics/GraphicsContextState.h"
 #include "platform/graphics/skia/OpaqueRegionSkia.h"
 #include "wtf/FastAllocBase.h"
@@ skipping 491 matching lines @@
     bool m_updatingControlTints : 1;
     bool m_accelerated : 1;
     bool m_isCertainlyOpaque : 1;
     bool m_printing : 1;
     bool m_antialiasHairlineImages : 1;
 };
 
 } // namespace WebCore
 
 #endif // GraphicsContext_h