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 b77cd9cdd5d85952380270c85d1ecfa4c9cc2b12..46051104a76cbe9cffd62579f2b9b357cf26c737 100644
--- a/Source/core/platform/graphics/GraphicsLayer.h
+++ b/Source/core/platform/graphics/GraphicsLayer.h
@@ -226,7 +226,7 @@ public:
     void setContentsToNinePatch(Image*, const IntRect& aperture);
     bool shouldDirectlyCompositeImage(Image*) const { return true; }
     // Pass an invalid color to remove the contents layer.
-    void setContentsToSolidColor(const Color&) { }
+    void setContentsToSolidColor(const Color&);
     void setContentsToPlatformLayer(blink::WebLayer* layer) { setContentsTo(layer); }
     bool hasContentsLayer() const { return m_contentsLayer; }
 
@@ -269,11 +269,6 @@ public:
     void resetTrackedRepaints();
     void addRepaintRect(const FloatRect&);
 
-    static bool supportsBackgroundColorContent()
-    {
-        return false;
-    }
-
     void addLinkHighlight(LinkHighlightClient*);
     void removeLinkHighlight(LinkHighlightClient*);
     // Exposed for tests
@@ -384,6 +379,8 @@ 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,