Give the main frame a RenderWidget.

content/public/browser/web_contents.h

 // Copyright (c) 2012 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_PUBLIC_BROWSER_WEB_CONTENTS_H_
 #define CONTENT_PUBLIC_BROWSER_WEB_CONTENTS_H_
 
 #include <set>
 
 #include "base/basictypes.h"
@@ skipping 94 matching lines @@
     // If the opener is suppressed, then the new WebContents doesn't hold a
     // reference to its opener.
     bool opener_suppressed;
 
     // Indicates whether this WebContents was created with a window.opener.
     // This is used when determining whether the WebContents is allowed to be
     // closed via window.close(). This may be true even with a null |opener|
     // (e.g., for blocked popups).
     bool created_with_opener;
 
-    // The routing ids of the RenderView and of the main RenderFrame. Either
-    // both must be provided, or both must be MSG_ROUTING_NONE to have the
-    // WebContents make the assignment.
-    int routing_id;
-    int main_frame_routing_id;
+    // The routing ids of the RenderView, main RenderFrame, and the widget for
+    // the main RenderFrame. Either all routing IDs must be provided or all must
+    // be MSG_ROUTING_NONE to have WebContents make the assignment.

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

Maybe the documentation should probably say which process_id these route_ids are
for (it's the opener's process -- at least I pray it is -- right?).

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

Done, though it's actually for site_instance->GetProcess()->GetID().

+    int32 routing_id;
+    int32 main_frame_routing_id;
+    int32 main_frame_widget_routing_id;
+
+    // The surface ID of the main frame widget.

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

Add a comment saying when this must be provided (it's required when we have a
widget_routing_id, right?).

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

Done.

+    int32 surface_id;
 
     // The name of the top-level frame of the new window. It is non-empty
     // when creating a named window (e.g. <a target="foo"> or
     // window.open('', 'bar')).
     std::string main_frame_name;
 
     // Initial size of the new WebContent's view. Can be (0, 0) if not needed.
     gfx::Size initial_size;
 
     // True if the contents should be initially hidden.
@@ skipping 561 matching lines @@
 
  private:
   // This interface should only be implemented inside content.
   friend class WebContentsImpl;
   WebContents() {}
 };
 
 }  // namespace content
 
 #endif  // CONTENT_PUBLIC_BROWSER_WEB_CONTENTS_H_