Add WebWidgetTestProxy.

third_party/WebKit/public/web/WebFrameWidget.h

Index: third_party/WebKit/public/web/WebFrameWidget.h
diff --git a/third_party/WebKit/public/web/WebFrameWidget.h b/third_party/WebKit/public/web/WebFrameWidget.h
index 6db89b5001187e04dd961a26ea619899ff3cc86a..43c6ddf9d72317144d377d37d6c8fcd2dab41c06 100644
--- a/third_party/WebKit/public/web/WebFrameWidget.h
+++ b/third_party/WebKit/public/web/WebFrameWidget.h
@@ -69,6 +69,12 @@ public:
     // persists across subsequent navigations. Defaults to white prior to the
     // first call to this method.
     virtual void setBaseBackgroundColor(WebColor) = 0;
+
+    // Returns the local root of this WebFrameWidget.
+    virtual WebLocalFrame* localRoot() = 0;
+
+    // WebWidget implementation.
+    bool isWebFrameWidget() const final { return true; }
 };
 
 } // namespace blink