Adding backgroundColor to WebCompositionUnderline and using it for InlineTextBox drawing.

Source/core/editing/CompositionUnderline.h

 /*
  * Copyright (C) 2006, 2007, 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
@@ skipping 14 matching lines @@
 
 #ifndef CompositionUnderline_h
 #define CompositionUnderline_h
 
 #include "platform/graphics/Color.h"
 
 namespace WebCore {
 
 struct CompositionUnderline {
     CompositionUnderline()
-        : startOffset(0), endOffset(0), thick(false) { }
+        : startOffset(0)
+        , endOffset(0)
+        , color(Color::transparent)
+        , thick(false)
+        , backgroundColor(Color::transparent) { }
+
+    // FIXME(huangs): remove this constructor.
     CompositionUnderline(unsigned s, unsigned e, const Color& c, bool t)
-        : startOffset(s), endOffset(e), color(c), thick(t) { }
+        : startOffset(s)
+        , endOffset(e)
+        , color(c)
+        , thick(t)
+        , backgroundColor(Color::transparent) { }
+
+    CompositionUnderline(unsigned s, unsigned e, const Color& c, bool t, const Color& bc)
+        : startOffset(s)
+        , endOffset(e)
+        , color(c)
+        , thick(t)
+        , backgroundColor(bc) { }
+
     unsigned startOffset;
     unsigned endOffset;
     Color color;
     bool thick;
+    Color backgroundColor;
 };
 
 } // namespace WebCore
 
 #endif // CompositionUnderline_h