Prefer to forward-declare GraphicsContext in headers.

Source/core/css/CSSPrimitiveValue.cpp

 /*
  * (C) 1999-2003 Lars Knoll (knoll@kde.org)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2012 Apple Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
  * This library is distributed in the hope that it will be useful,
@@ skipping 19 matching lines @@
 #include "core/css/Counter.h"
 #include "core/css/Pair.h"
 #include "core/css/RGBColor.h"
 #include "core/css/Rect.h"
 #include "core/css/StyleSheetContents.h"
 #include "core/dom/ExceptionCode.h"
 #include "core/dom/Node.h"
 #include "core/rendering/style/RenderStyle.h"
 #include "platform/Decimal.h"
 #include "platform/LayoutUnit.h"
+#include "platform/fonts/FontMetrics.h"
 #include "wtf/StdLibExtras.h"
 #include "wtf/text/StringBuffer.h"
 #include "wtf/text/StringBuilder.h"
 
 using namespace WTF;
 
 namespace WebCore {
 
 // Max/min values for CSS, needs to slightly smaller/larger than the true max/min values to allow for rounding without overflowing.
 // Subtract two (rather than one) to allow for values to be converted to float and back without exceeding the LayoutUnit::max.
@@ skipping 1381 matching lines @@
     case CSS_SHAPE:
         visitor->trace(m_value.shape);
         break;
     default:
         break;
     }
     CSSValue::traceAfterDispatch(visitor);
 }
 
 } // namespace WebCore