Prefer to forward-declare GraphicsContext in headers.

Source/core/rendering/RenderScrollbarTheme.cpp

 /*
  * Copyright (C) 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
  *    notice, this list of conditions and the following disclaimer in the
  *    documentation and/or other materials provided with the distribution.
  *
  * THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
  * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
  * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE INC. OR
  * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
  * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT 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 "core/rendering/RenderScrollbar.h"
 #include "core/rendering/RenderScrollbarTheme.h"
+#include "platform/graphics/GraphicsContext.h"
 #include "platform/scroll/ScrollbarThemeClient.h"
 #include "wtf/StdLibExtras.h"
 
 namespace WebCore {
 
 RenderScrollbarTheme* RenderScrollbarTheme::renderScrollbarTheme()
 {
     DEFINE_STATIC_LOCAL(RenderScrollbarTheme, theme, ());
     return &theme;
 }
@@ skipping 98 matching lines @@
 {
     toRenderScrollbar(scrollbar)->paintPart(context, ThumbPart, rect);
 }
 
 void RenderScrollbarTheme::paintTickmarks(GraphicsContext* context, ScrollbarThemeClient* scrollbar, const IntRect& rect)
 {
     ScrollbarTheme::theme()->paintTickmarks(context, scrollbar, rect);
 }
 
 }