Give the main frame a RenderWidget.

content/browser/frame_host/render_frame_host_manager.h

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CONTENT_BROWSER_FRAME_HOST_RENDER_FRAME_HOST_MANAGER_H_
 #define CONTENT_BROWSER_FRAME_HOST_RENDER_FRAME_HOST_MANAGER_H_
 
 #include <list>
 #include <map>
 
@@ skipping 184 matching lines @@
   // You must call Init() before using this class.
   RenderFrameHostManager(
       FrameTreeNode* frame_tree_node,
       RenderFrameHostDelegate* render_frame_delegate,
       RenderViewHostDelegate* render_view_delegate,
       RenderWidgetHostDelegate* render_widget_delegate,
       Delegate* delegate);
   ~RenderFrameHostManager();
 
   // For arguments, see WebContentsImpl constructor.
-  void Init(BrowserContext* browser_context,
-            SiteInstance* site_instance,
+  // TODO(dcheng): |site_instance| should probably be a const scoped_refptr<>&.

[ncarter (slow), 2015/09/03 20:24:37]

I think this is worth contemplating, but I don't think it's worth a TODO
comment.

[dcheng, 2015/09/03 21:29:24]

Comment removed.

+  void Init(SiteInstance* site_instance,
             int32 view_routing_id,
             int32 frame_routing_id,
             int32 widget_routing_id,
             int32 surface_id);
 
   // Returns the currently active RenderFrameHost.
   //
   // This will be non-NULL between Init() and Shutdown(). You may want to NULL
   // check it in many cases, however. Windows can send us messages during the
   // destruction process after it has been shut down.
@@ skipping 602 matching lines @@
   bool should_reuse_web_ui_;
 
   base::WeakPtrFactory<RenderFrameHostManager> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(RenderFrameHostManager);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_FRAME_HOST_RENDER_FRAME_HOST_MANAGER_H_