Snapshot a pointer to the main frame when creating WebViewFrameWidget.

public/web/WebFrameWidget.h

Index: public/web/WebFrameWidget.h
diff --git a/public/web/WebFrameWidget.h b/public/web/WebFrameWidget.h
index df4212fc5263f4bae3a65bc197dbdeecb28650b9..474bcf2466fff5b4a822556350e314eb6f117d22 100644
--- a/public/web/WebFrameWidget.h
+++ b/public/web/WebFrameWidget.h
@@ -46,7 +46,8 @@ public:
     BLINK_EXPORT static WebFrameWidget* create(WebWidgetClient*, WebLocalFrame*);
     // Creates a frame widget for a WebView. Temporary helper to help transition
     // away from WebView inheriting WebWidget.
-    BLINK_EXPORT static WebFrameWidget* create(WebView*);
+    // TODO(dcheng): Remove once transition is complete.
+    BLINK_EXPORT static WebFrameWidget* create(WebWidgetClient*, WebView*, WebLocalFrame* mainFrame);
 
     // Sets the visibility of the WebFrameWidget.
     // We still track page-level visibility, but additionally we need to notify a WebFrameWidget