Adding backgroundColor to WebCompositionUnderline and using it for InlineTextBox drawing.

Source/core/rendering/InlineTextBox.h

Index: Source/core/rendering/InlineTextBox.h
diff --git a/Source/core/rendering/InlineTextBox.h b/Source/core/rendering/InlineTextBox.h
index e2db766e70651e7a02db6eeb35644edb2025e861..3cfa5ec9b2fa208f5b5cc40afdd84263ce0277d2 100644
--- a/Source/core/rendering/InlineTextBox.h
+++ b/Source/core/rendering/InlineTextBox.h
@@ -175,8 +175,12 @@ private:
     unsigned short m_truncation; // Where to truncate when text overflow is applied.  We use special constants to
                       // denote no truncation (the whole run paints) and full truncation (nothing paints at all).
 
+    unsigned underlinePaintStart(const CompositionUnderline&);
+    unsigned underlinePaintEnd(const CompositionUnderline&);
+
 protected:
-    void paintCompositionBackground(GraphicsContext*, const FloatPoint& boxOrigin, RenderStyle*, const Font&, int startPos, int endPos);
+    void paintSingleCompositionBackgroundRun(GraphicsContext*, const FloatPoint& boxOrigin, RenderStyle*, const Font&, Color backgroundColor, int startPos, int endPos);
+    void paintCompositionBackgrounds(GraphicsContext*, const FloatPoint& boxOrigin, RenderStyle*, const Font&, bool useCustomUnderlines);
     void paintDocumentMarkers(GraphicsContext*, const FloatPoint& boxOrigin, RenderStyle*, const Font&, bool background);
     void paintCompositionUnderline(GraphicsContext*, const FloatPoint& boxOrigin, const CompositionUnderline&);