Adding backgroundColor to WebCompositionUnderline and using it for InlineTextBox drawing.

public/web/WebCompositionUnderline.h

Index: public/web/WebCompositionUnderline.h
diff --git a/public/web/WebCompositionUnderline.h b/public/web/WebCompositionUnderline.h
index 2c5866205375ca6cab9e649b613c4fa047e9a837..21c065ba4871de539c20e9446311c05960bcc77d 100644
--- a/public/web/WebCompositionUnderline.h
+++ b/public/web/WebCompositionUnderline.h
@@ -42,18 +42,36 @@ struct WebCompositionUnderline {
         : startOffset(0)
         , endOffset(0)
         , color(0)
-        , thick(false) { }
+        , thick(false)
+        , backgroundColor(0) { }
 
+    // FIXME(huangs): remove this constructor.
     WebCompositionUnderline(unsigned s, unsigned e, WebColor c, bool t)
         : startOffset(s)
         , endOffset(e)
         , color(c)
-        , thick(t) { }
+        , thick(t)
+        , backgroundColor(0) { }
 
+    WebCompositionUnderline(unsigned s, unsigned e, WebColor c, bool t, WebColor bc)
+        : startOffset(s)
+        , endOffset(e)
+        , color(c)
+        , thick(t)
+        , backgroundColor(bc) { }
+
+    bool operator<(const WebCompositionUnderline& other) const
+    {
+        return startOffset != other.startOffset ? startOffset < other.startOffset : endOffset < other.endOffset;
+    }
+
+    // Need to update IPC_STRUCT_TRAITS_BEGIN(blink::WebCompositionUnderline)
+    // if members change.
     unsigned startOffset;
     unsigned endOffset;
     WebColor color;
     bool thick;
+    WebColor backgroundColor;
 };
 
 } // namespace blink