Attach a WebLayer to a frame element for out-of-process iframes.

Source/core/rendering/CompositedLayerMapping.cpp

Index: Source/core/rendering/CompositedLayerMapping.cpp
diff --git a/Source/core/rendering/CompositedLayerMapping.cpp b/Source/core/rendering/CompositedLayerMapping.cpp
index a5ecbffd96fcc5b94fc979a105d97674c365d71a..49cf29cb9f1c73e191c23c9197eabc8ecf67374a 100644
--- a/Source/core/rendering/CompositedLayerMapping.cpp
+++ b/Source/core/rendering/CompositedLayerMapping.cpp
@@ -504,6 +504,10 @@ bool CompositedLayerMapping::updateGraphicsLayerConfiguration()
     if (renderer->isEmbeddedObject() && toRenderEmbeddedObject(renderer)->allowsAcceleratedCompositing()) {
         PluginView* pluginView = toPluginView(toRenderWidget(renderer)->widget());
         m_graphicsLayer->setContentsToPlatformLayer(pluginView->platformLayer());
+    } else if (renderer->node()->isFrameOwnerElement() && toHTMLFrameOwnerElement(renderer->node())->contentFrame()) {
+        blink::WebLayer* layer = toHTMLFrameOwnerElement(renderer->node())->contentFrame()->remotePlatformLayer();
+        if (layer)
+            m_graphicsLayer->setContentsToPlatformLayer(layer);
     } else if (renderer->isVideo()) {
         HTMLMediaElement* mediaElement = toHTMLMediaElement(renderer->node());
         m_graphicsLayer->setContentsToPlatformLayer(mediaElement->platformLayer());