Adding backgroundColor to WebCompositionUnderline and using it for InlineTextBox drawing.

Source/core/editing/CompositionUnderline.h

Index: Source/core/editing/CompositionUnderline.h
diff --git a/Source/core/editing/CompositionUnderline.h b/Source/core/editing/CompositionUnderline.h
index 025ee75cbf7696170769d5531c0891a254fb2681..54bbad2f499bb04cb077b2774dce96093fe09a94 100644
--- a/Source/core/editing/CompositionUnderline.h
+++ b/Source/core/editing/CompositionUnderline.h
@@ -32,13 +32,32 @@ 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