Give the main frame a RenderWidget.

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 ba49c52e4c9a99839cca929742f0b1f501cbc85b..e97b2df32d7ae50c32faf034ca0782708ebf926f 100644
--- a/content/renderer/render_frame_impl.h
+++ b/content/renderer/render_frame_impl.h
@@ -65,6 +65,7 @@ class WebSecurityOrigin;
 struct WebCompositionUnderline;
 struct WebContextMenuData;
 struct WebCursorInfo;
+struct WebScreenInfo;
 }
 
 namespace gfx {
@@ -128,14 +129,16 @@ class CONTENT_EXPORT RenderFrameImpl
       NON_EXPORTED_BASE(public blink::WebFrameClient),
       NON_EXPORTED_BASE(public media::WebMediaPlayerDelegate) {
  public:
-  // Creates a new RenderFrame. |render_view| is the RenderView object that this
-  // frame belongs to.
-  // Callers *must* call |SetWebFrame| immediately after creation.
-  // Note: This is called only when RenderFrame is created by Blink through
-  // createChildFrame.
-  // TODO(creis): We should structure this so that |SetWebFrame| isn't needed.
-  static RenderFrameImpl* Create(RenderViewImpl* render_view, int32 routing_id);
-
+  static RenderFrameImpl* CreateMainFrame(
+      RenderViewImpl* render_view,
+      int32 routing_id,
+      int32 widget_routing_id,
+      int32 surface_id,
+      bool hidden,
+      const blink::WebScreenInfo& screen_info,
+      CompositorDependencies* compositor_deps);
+
+  // TODO(dcheng): This should probably be renamed to CreateChildFrame.

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

I agree. There are only two callers, so I think you should just go ahead and
make the fix.

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

It turns out this isn't just used for subframes, so I've deleted this TODO.

   // Creates a new RenderFrame with |routing_id| as a child of the RenderFrame
   // identified by |parent_routing_id| or as the top-level frame if the latter
   // is MSG_ROUTING_NONE. If |proxy_routing_id| is MSG_ROUTING_NONE, it creates
@@ -624,6 +627,11 @@ class CONTENT_EXPORT RenderFrameImpl
 
   typedef std::map<GURL, double> HostZoomLevels;
 
+  // Creates a new RenderFrame. |render_view| is the RenderView object that this
+  // frame belongs to.
+  // Callers *must* call |SetWebFrame| immediately after creation.
+  static RenderFrameImpl* Create(RenderViewImpl* render_view, int32 routing_id);
+
   // Functions to add and remove observers for this object.
   void AddObserver(RenderFrameObserver* observer);
   void RemoveObserver(RenderFrameObserver* observer);