Prefer to forward-declare GraphicsContext in headers.

Source/platform/scroll/ScrollbarThemeMacNonOverlayAPI.mm

 /*
  * 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:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 13 matching lines @@
  * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  * DATA, OR 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/scroll/ScrollbarThemeMacNonOverlayAPI.h"
 
-#include <Carbon/Carbon.h>
+#include "platform/graphics/GraphicsContext.h"
 #include "platform/graphics/ImageBuffer.h"
 #include "platform/scroll/ScrollbarThemeClient.h"
 #include "public/platform/Platform.h"
 #include "public/platform/WebRect.h"
 #include "public/platform/WebThemeEngine.h"
 #include "skia/ext/skia_utils_mac.h"
+#include <Carbon/Carbon.h>
 
 namespace WebCore {
 
 // FIXME: Get these numbers from CoreUI.
 static int cRealButtonLength[] = { 28, 21 };
 static int cButtonHitInset[] = { 3, 2 };
 // cRealButtonLength - cButtonInset
 static int cButtonLength[] = { 14, 10 };
 static int cScrollbarThickness[] = { 15, 11 };
 static int cButtonInset[] = { 14, 11 };
@@ skipping 282 matching lines @@
         return IntRect(scrollbar->x() + startWidth, scrollbar->y(), scrollbar->width() - totalWidth, thickness);
     return IntRect(scrollbar->x(), scrollbar->y() + startWidth, thickness, scrollbar->height() - totalWidth);
 }
 
 int ScrollbarThemeMacNonOverlayAPI::minimumThumbLength(ScrollbarThemeClient* scrollbar)
 {
     return cThumbMinLength[scrollbar->controlSize()];
 }
 
 }