Give the main frame a RenderWidget.

chrome/browser/android/document/document_web_contents_delegate.h

Index: chrome/browser/android/document/document_web_contents_delegate.h
diff --git a/chrome/browser/android/document/document_web_contents_delegate.h b/chrome/browser/android/document/document_web_contents_delegate.h
index cba342b8dfcd048020be792ea10437669cc84d20..043769d6c5af399fd98350588c84efbd04337444 100644
--- a/chrome/browser/android/document/document_web_contents_delegate.h
+++ b/chrome/browser/android/document/document_web_contents_delegate.h
@@ -36,8 +36,9 @@ class DocumentWebContentsDelegate
   void CloseContents(content::WebContents* source) override;
   bool ShouldCreateWebContents(
       content::WebContents* web_contents,
-      int route_id,
-      int main_frame_route_id,
+      int32 route_id,

[sky, 2015/10/22 23:05:47]

int32->int32_t (the non _t types are deprecated, see comment in
base/basictypes.h). I'm only commenting on this here, no doubt you'll need to
update a bunch of places.

[dcheng, 2015/10/22 23:29:44]

This was intentional, to keep code in //content consistent (this code lives next
to a bunch of unchanged code that uses int32). If you feel strongly, I can
update.

+      int32 main_frame_route_id,
+      int32 main_frame_widget_route_id,
       WindowContainerType window_container_type,
       const std::string& frame_name,
       const GURL& target_url,