Adding backgroundColor to WebCompositionUnderline and using it for InlineTextBox drawing.

Source/core/rendering/RenderTheme.h

 /*
  * This file is part of the theme implementation for form controls in WebCore.
  *
  * Copyright (C) 2005, 2006, 2007, 2008, 2009, 2010, 2012 Apple Computer, Inc.
  *
  * 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.
  *
@@ skipping 123 matching lines @@
 
     // Highlighting colors for TextMatches.
     virtual Color platformActiveTextSearchHighlightColor() const;
     virtual Color platformInactiveTextSearchHighlightColor() const;
 
     Color focusRingColor() const;
     virtual Color platformFocusRingColor() const { return Color(0, 0, 0); }
     void setCustomFocusRingColor(const Color&);
     static Color tapHighlightColor();
     virtual Color platformTapHighlightColor() const { return RenderTheme::defaultTapHighlightColor; }
+    virtual Color platformDefaultCompositionBackgroundColor() const { return defaultCompositionBackgroundColor; }
     virtual void platformColorsDidChange();
 
     virtual double caretBlinkInterval() const { return 0.5; }
 
     // System fonts and colors for CSS.
     virtual void systemFont(CSSValueID, FontDescription&) const = 0;
     virtual Color systemColor(CSSValueID) const;
 
     virtual int minimumMenuListSize(RenderStyle*) const { return 0; }
 
@@ skipping 145 matching lines @@
     bool isReadOnlyControl(const RenderObject*) const;
 
 private:
     Color m_customFocusRingColor;
     bool m_hasCustomFocusRingColor;
 
     // This color is expected to be drawn on a semi-transparent overlay,
     // making it more transparent than its alpha value indicates.
     static const RGBA32 defaultTapHighlightColor = 0x66000000;
 
+    static const RGBA32 defaultCompositionBackgroundColor = 0xFFFFDD55;
+
 #if USE(NEW_THEME)
     Theme* m_platformTheme; // The platform-specific theme.
 #endif
 };
 
 } // namespace WebCore
 
 #endif // RenderTheme_h