Give the main frame a RenderWidget.

content/renderer/render_widget.cc

Index: content/renderer/render_widget.cc
diff --git a/content/renderer/render_widget.cc b/content/renderer/render_widget.cc
index a071d1477ad0e8e6c6e6962b95285a313368c79f..b76f515ab7468f409a1039c92f9af485ba0d33fd 100644
--- a/content/renderer/render_widget.cc
+++ b/content/renderer/render_widget.cc
@@ -587,6 +587,11 @@ RenderWidget* RenderWidget::CreateForFrame(
 blink::WebWidget* RenderWidget::CreateWebFrameWidget(
     RenderWidget* render_widget,
     blink::WebLocalFrame* frame) {
+  if (!frame->parent()) {
+    // TODO(dcheng): The main frame widget currently has a special case.
+    // Eliminate this once WebView is no longer a WebWidget.
+    return blink::WebFrameWidget::create(render_widget, frame->view(), frame);
+  }
   return blink::WebFrameWidget::create(render_widget, frame);
 }