Make RenderFrame(Host) own a RenderWidget(Host).

content/renderer/render_frame_impl.h

Index: content/renderer/render_frame_impl.h
diff --git a/content/renderer/render_frame_impl.h b/content/renderer/render_frame_impl.h
index be85ce971d685ae9050ac01e2257090aff96a541..3d3fbe645e98af026b59c6ee03d52f9bbd3d86c1 100644
--- a/content/renderer/render_frame_impl.h
+++ b/content/renderer/render_frame_impl.h
@@ -499,6 +499,7 @@ class CONTENT_EXPORT RenderFrameImpl
   // content/common/*_messages.h for the message that the function is handling.
   void OnBeforeUnload();
   void OnSwapOut(int proxy_routing_id);
+  void OnNewWidgetForFrame(int routing_id_for_widget, bool hidden);
   void OnStop();
   void OnShowContextMenu(const gfx::Point& location);
   void OnContextMenuClosed(const CustomContextMenuContext& custom_context);
@@ -638,6 +639,9 @@ class CONTENT_EXPORT RenderFrameImpl
   RenderFrameProxy* render_frame_proxy_;
   bool is_detaching_;
 
+  // Used when the RenderFrame is a root of a subtree of local frames.

[nasko, 2014/10/01 16:37:14]

nit: the subtree needn't all be local frames, right? We can have
Remote->(this)Local->Remote and we will still need a widget for this frame. If
the parent is remote, then we need a widget, right?

[kenrb, 2014/10/01 19:27:51]

Okay. Changed 'subtree' to 'connected subtree'.

+  scoped_refptr<RenderWidget> render_widget_;
+
 #if defined(ENABLE_PLUGINS)
   // Current text input composition text. Empty if no composition is in
   // progress.