Make <webview> use out-of-process iframe architecture.

extensions/renderer/guest_view/extensions_guest_view_container.h

Index: extensions/renderer/guest_view/extensions_guest_view_container.h
diff --git a/extensions/renderer/guest_view/extensions_guest_view_container.h b/extensions/renderer/guest_view/extensions_guest_view_container.h
index 0a29daf22c4210008a7e37abd20d48bb267f0100..5b5859a588754882f6351329cca3f3bf66e4c383 100644
--- a/extensions/renderer/guest_view/extensions_guest_view_container.h
+++ b/extensions/renderer/guest_view/extensions_guest_view_container.h
@@ -26,6 +26,9 @@ class ExtensionsGuestViewContainer : public GuestViewContainer {
   void RegisterElementResizeCallback(v8::Local<v8::Function> callback,
                                      v8::Isolate* isolate);
 
+  // GuestViewContainer overrides.
+  bool OnMessage(const IPC::Message& message) override;
+
   // BrowserPluginDelegate implementation.
   void DidResizeElement(const gfx::Size& old_size,
                         const gfx::Size& new_size) override;