Prefer to forward-declare GraphicsContext in headers.

Source/platform/scroll/ScrollbarTheme.cpp

 /*
  * Copyright (C) 2011 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
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 10 matching lines @@
  * 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/scroll/ScrollbarTheme.h"
 
 #include "RuntimeEnabledFeatures.h"
 #include "platform/PlatformMouseEvent.h"
+#include "platform/graphics/Color.h"
+#include "platform/graphics/GraphicsContext.h"
 #include "platform/scroll/ScrollbarThemeClient.h"
 #include "platform/scroll/ScrollbarThemeMock.h"
 #include "platform/scroll/ScrollbarThemeOverlayMock.h"
 #include "public/platform/Platform.h"
 #include "public/platform/WebPoint.h"
 #include "public/platform/WebRect.h"
 #include "public/platform/WebScrollbarBehavior.h"
 
 #if !OS(MACOSX)
 #include "public/platform/WebRect.h"
@@ skipping 308 matching lines @@
 {
     gMockScrollbarsEnabled = flag;
 }
 
 bool ScrollbarTheme::mockScrollbarsEnabled()
 {
     return gMockScrollbarsEnabled;
 }
 
 }