Re-enable solid background color optimization for composited layers.

Source/core/platform/graphics/GraphicsLayer.h

Index: Source/core/platform/graphics/GraphicsLayer.h
diff --git a/Source/core/platform/graphics/GraphicsLayer.h b/Source/core/platform/graphics/GraphicsLayer.h
index d4b002c03cff0927e829732f63f2f99fb32406f3..4e8ba0e75c24b5e4fd2907aed904f2fee3d29b91 100644
--- a/Source/core/platform/graphics/GraphicsLayer.h
+++ b/Source/core/platform/graphics/GraphicsLayer.h
@@ -227,7 +227,7 @@ public:
     bool shouldDirectlyCompositeImage(Image*) const { return true; }
     void setContentsToMedia(blink::WebLayer*); // video or plug-in
     // Pass an invalid color to remove the contents layer.
-    void setContentsToSolidColor(const Color&) { }
+    void setContentsToSolidColor(const Color&);
     void setContentsToCanvas(blink::WebLayer*);
     // FIXME: webkit.org/b/109658
     // Should unify setContentsToMedia and setContentsToCanvas
@@ -273,11 +273,6 @@ public:
     void resetTrackedRepaints();
     void addRepaintRect(const FloatRect&);
 
-    static bool supportsBackgroundColorContent()
-    {
-        return false;
-    }
-
     void addLinkHighlight(LinkHighlightClient*);
     void removeLinkHighlight(LinkHighlightClient*);
     // Exposed for tests
@@ -388,6 +383,8 @@ private:
     OwnPtr<blink::WebContentLayer> m_layer;
     OwnPtr<blink::WebImageLayer> m_imageLayer;
     OwnPtr<blink::WebNinePatchLayer> m_ninePatchLayer;
+    Color m_contentsSolidColor;
+    OwnPtr<blink::WebSolidColorLayer> m_solidColorLayer;
     blink::WebLayer* m_contentsLayer;
     // We don't have ownership of m_contentsLayer, but we do want to know if a given layer is the
     // same as our current layer in setContentsTo(). Since m_contentsLayer may be deleted at this point,