Re-enable solid background color optimization for composited layers.

Source/core/platform/graphics/GraphicsLayer.cpp

Index: Source/core/platform/graphics/GraphicsLayer.cpp
diff --git a/Source/core/platform/graphics/GraphicsLayer.cpp b/Source/core/platform/graphics/GraphicsLayer.cpp
index f48c07505835007c8d86a93dc5c70bfdbabb14ed..1e8be8daa6f70fc7b57905a6a43c74f07b6aaec3 100644
--- a/Source/core/platform/graphics/GraphicsLayer.cpp
+++ b/Source/core/platform/graphics/GraphicsLayer.cpp
@@ -995,6 +995,27 @@ void GraphicsLayer::setContentsToNinePatch(Image* image, const IntRect& aperture
     setContentsTo(m_ninePatchLayer ? m_ninePatchLayer->layer() : 0);
 }
 
+void GraphicsLayer::setContentsToSolidColor(const Color& color)
+{
+    if (color == m_contentsSolidColor)
+        return;
+
+    m_contentsSolidColor = color;
+    if (color.isValid() && color.alpha()) {
+        if (!m_solidColorLayer) {
+            m_solidColorLayer = adoptPtr(Platform::current()->compositorSupport()->createSolidColorLayer());
+            registerContentsLayer(m_solidColorLayer->layer());
+        }
+        m_solidColorLayer->setBackgroundColor(color.rgb());
+    } else {
+        if (!m_solidColorLayer)
+            return;
+        unregisterContentsLayer(m_solidColorLayer->layer());
+        m_solidColorLayer.clear();
+    }
+    setContentsTo(m_solidColorLayer ? m_solidColorLayer->layer() : 0);
+}
+
 void GraphicsLayer::setContentsToCanvas(WebLayer* layer)
 {
     setContentsTo(layer);