Give the main frame a RenderWidget.

content/common/view_messages.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.
 
 // IPC messages for page rendering.
 // Multiply-included message file, hence no include guard.
 
 #include "base/memory/shared_memory.h"
 #include "base/process/process.h"
 #include "base/strings/string16.h"
@@ skipping 342 matching lines @@
 
   // The window features to use for the new view.
   IPC_STRUCT_MEMBER(blink::WebWindowFeatures, features)
 
   // The additional window features to use for the new view. We pass these
   // separately from |features| above because we cannot serialize WebStrings
   // over IPC.
   IPC_STRUCT_MEMBER(std::vector<base::string16>, additional_features)
 IPC_STRUCT_END()
 
+IPC_STRUCT_BEGIN(ViewHostMsg_CreateWindow_Reply)
+  IPC_STRUCT_MEMBER(int32, route_id)

[dcheng, 2015/08/24 18:50:20]

I used the non _t versions to be consistent with what's already present in this
file.

+  IPC_STRUCT_MEMBER(int32, main_frame_route_id)
+  IPC_STRUCT_MEMBER(int32, main_frame_widget_route_id)
+  IPC_STRUCT_MEMBER(int32, surface_id)
+  IPC_STRUCT_MEMBER(int64, cloned_session_storage_namespace_id)
+IPC_STRUCT_END()

[ncarter (slow), 2015/08/24 20:55:35]

Can you add comments to these IPC_STRUCT_MEMBERS? In particular I'd like some
description to help differentiate the objects the various route_id's correspond
to.

[dcheng, 2015/09/03 16:33:09]

Done.

+
 IPC_STRUCT_BEGIN(ViewHostMsg_CreateWorker_Params)
   // URL for the worker script.
   IPC_STRUCT_MEMBER(GURL, url)
 
   // Name for a SharedWorker, otherwise empty string.
   IPC_STRUCT_MEMBER(base::string16, name)
 
   // Security policy used in the worker.
   IPC_STRUCT_MEMBER(base::string16, content_security_policy)
 
@@ skipping 124 matching lines @@
 
   // Preferences for this view.
   IPC_STRUCT_MEMBER(content::WebPreferences, web_preferences)
 
   // The ID of the view to be created.
   IPC_STRUCT_MEMBER(int32, view_id)
 
   // The ID of the main frame hosted in the view.
   IPC_STRUCT_MEMBER(int32, main_frame_routing_id)
 
+  // The ID of the widget for the main frame.
+  IPC_STRUCT_MEMBER(int32, main_frame_widget_routing_id)
+
   // The ID of the rendering surface.
   IPC_STRUCT_MEMBER(int32, surface_id)
 
   // The session storage namespace ID this view should use.
   IPC_STRUCT_MEMBER(int64, session_storage_namespace_id)
 
   // The route ID of the opener RenderFrame or RenderFrameProxy, if we need to
   // set one (MSG_ROUTING_NONE otherwise).
   IPC_STRUCT_MEMBER(int, opener_frame_route_id)
 
@@ skipping 475 matching lines @@
 // -----------------------------------------------------------------------------
 // Messages sent from the renderer to the browser.
 
 // Sent by renderer to request a ViewMsg_BeginFrame message for upcoming
 // display events. If |enabled| is true, the BeginFrame message will continue
 // to be be delivered until the notification is disabled.
 IPC_MESSAGE_ROUTED1(ViewHostMsg_SetNeedsBeginFrames,
                     bool /* enabled */)
 
 // Sent by the renderer when it is creating a new window.  The browser creates
 // a tab for it and responds with a ViewMsg_CreatingNew_ACK.  If route_id is

[ncarter (slow), 2015/08/24 20:55:35]

This comment about "route_id" is stale.

[dcheng, 2015/09/03 16:33:09]

I've moved this comment to ViewHsotMsg_CreateWindow_Reply.

 // MSG_ROUTING_NONE, the view couldn't be created.
-IPC_SYNC_MESSAGE_CONTROL1_4(ViewHostMsg_CreateWindow,
+IPC_SYNC_MESSAGE_CONTROL1_1(ViewHostMsg_CreateWindow,
                             ViewHostMsg_CreateWindow_Params,
-                            int /* route_id */,
-                            int /* main_frame_route_id */,
-                            int32 /* surface_id */,
-                            int64 /* cloned_session_storage_namespace_id */)
+                            ViewHostMsg_CreateWindow_Reply)

[dcheng, 2015/08/24 18:50:20]

IPCs can't have more than 4 out parameters. I wasn't able to find a good naming
convention for reply structs, so I just made something up

 
 // Similar to ViewHostMsg_CreateWindow, except used for sub-widgets, like
 // <select> dropdowns.  This message is sent to the WebContentsImpl that
 // contains the widget being created.
 IPC_SYNC_MESSAGE_CONTROL2_2(ViewHostMsg_CreateWidget,
                             int /* opener_id */,
                             blink::WebPopupType /* popup type */,
                             int /* route_id */,
                             int32 /* surface_id */)
 
@@ skipping 564 matching lines @@
 // cached by the OS. Please see RenderMessageFilter::OnPreCacheFontCharacters
 // for details.
 IPC_SYNC_MESSAGE_CONTROL2_0(ViewHostMsg_PreCacheFontCharacters,
                             LOGFONT /* font_data */,
                             base::string16 /* characters */)
 #endif
 
 // Adding a new message? Stick to the sort order above: first platform
 // independent ViewMsg, then ifdefs for platform specific ViewMsg, then platform
 // independent ViewHostMsg, then ifdefs for platform specific ViewHostMsg.