Cleanup RemotePlatformLayer when disconnecting RemoteFrame.

Source/core/rendering/compositing/CompositedLayerMapping.cpp

Index: Source/core/rendering/compositing/CompositedLayerMapping.cpp
diff --git a/Source/core/rendering/compositing/CompositedLayerMapping.cpp b/Source/core/rendering/compositing/CompositedLayerMapping.cpp
index d2001a5dfb27969921c85b632ab4003729352b22..19de1b34a56234f339bd8fecf2ff0bf87a6294db 100644
--- a/Source/core/rendering/compositing/CompositedLayerMapping.cpp
+++ b/Source/core/rendering/compositing/CompositedLayerMapping.cpp
@@ -30,6 +30,7 @@
 #include "core/HTMLNames.h"
 #include "core/fetch/ImageResource.h"
 #include "core/frame/FrameView.h"
+#include "core/frame/RemoteFrame.h"
 #include "core/html/HTMLCanvasElement.h"
 #include "core/html/HTMLIFrameElement.h"
 #include "core/html/HTMLMediaElement.h"
@@ -518,9 +519,10 @@ bool CompositedLayerMapping::updateGraphicsLayerConfiguration()
     if (WebLayer* layer = platformLayerForPlugin(renderer)) {
         m_graphicsLayer->setContentsToPlatformLayer(layer);
     } else if (renderer->node() && renderer->node()->isFrameOwnerElement() && toHTMLFrameOwnerElement(renderer->node())->contentFrame()) {
-        WebLayer* layer = toHTMLFrameOwnerElement(renderer->node())->contentFrame()->remotePlatformLayer();
-        if (layer)
+        if (toHTMLFrameOwnerElement(renderer->node())->contentFrame()->isRemoteFrame()) {
+            WebLayer* layer = toRemoteFrame(toHTMLFrameOwnerElement(renderer->node())->contentFrame())->remotePlatformLayer();
             m_graphicsLayer->setContentsToPlatformLayer(layer);
+        }
     } else if (renderer->isVideo()) {
         HTMLMediaElement* mediaElement = toHTMLMediaElement(renderer->node());
         m_graphicsLayer->setContentsToPlatformLayer(mediaElement->platformLayer());