Re-land "Drop background color optimization for composited layers"

Source/platform/graphics/GraphicsLayer.cpp

Index: Source/platform/graphics/GraphicsLayer.cpp
diff --git a/Source/platform/graphics/GraphicsLayer.cpp b/Source/platform/graphics/GraphicsLayer.cpp
index fb5821e2fdbd9992a3cfe5ead8556243f8fdddc3..0d58024c2da6e9a3feffa2635013895aa1e2f133 100644
--- a/Source/platform/graphics/GraphicsLayer.cpp
+++ b/Source/platform/graphics/GraphicsLayer.cpp
@@ -99,7 +99,6 @@ GraphicsLayer::GraphicsLayer(GraphicsLayerClient* client)
     , m_replicaLayer(0)
     , m_replicatedLayer(0)
     , m_paintCount(0)
-    , m_contentsSolidColor(Color::transparent)
     , m_contentsLayer(0)
     , m_contentsLayerId(0)
     , m_scrollableArea(0)
@@ -1026,27 +1025,6 @@ 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.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);
-}
-
 bool GraphicsLayer::addAnimation(PassOwnPtr<WebAnimation> popAnimation)
 {
     OwnPtr<WebAnimation> animation(popAnimation);