Give the main frame a RenderWidget.

content/renderer/render_view_impl.h

Index: content/renderer/render_view_impl.h
diff --git a/content/renderer/render_view_impl.h b/content/renderer/render_view_impl.h
index 3702a9267c9bddc8aeed5060e45d21baf2510ffb..175e9e09e91a9b368f3e336c305581a24fe5648a 100644
--- a/content/renderer/render_view_impl.h
+++ b/content/renderer/render_view_impl.h
@@ -48,6 +48,7 @@
 #include "third_party/WebKit/public/web/WebConsoleMessage.h"
 #include "third_party/WebKit/public/web/WebDataSource.h"
 #include "third_party/WebKit/public/web/WebElement.h"
+#include "third_party/WebKit/public/web/WebFrameWidget.h"
 #include "third_party/WebKit/public/web/WebHistoryItem.h"
 #include "third_party/WebKit/public/web/WebIconURL.h"
 #include "third_party/WebKit/public/web/WebInputEvent.h"
@@ -235,6 +236,8 @@ class CONTENT_EXPORT RenderViewImpl
   // Indicates whether this page has been focused by the browser.
   bool has_focus() const { return has_focus_; }
 
+  void AttachWebFrameWidget(blink::WebWidget* frame_widget);
+
   // Plugin-related functions --------------------------------------------------
 
 #if defined(ENABLE_PLUGINS)
@@ -445,6 +448,7 @@ class CONTENT_EXPORT RenderViewImpl
 
  protected:
   // RenderWidget overrides:
+  void CloseForFrame() override;
   void Close() override;
   void OnResize(const ViewMsg_Resize_Params& params) override;
   void DidInitiatePaint() override;
@@ -897,6 +901,10 @@ class CONTENT_EXPORT RenderViewImpl
 
   RenderFrameImpl* main_render_frame_;
 
+  // Note: RenderViewImpl is pulling double duty: it's the RenderWidget for the
+  // "view", but it's also the RenderWidget for the main frame.
+  blink::WebWidget* frame_widget_;
+
   // The next group of objects all implement RenderViewObserver, so are deleted
   // along with the RenderView automatically.  This is why we just store
   // weak references.