Add a debug view to the browser that allows various navigation features to be used.

services/navigation/view_impl.h

Index: services/navigation/view_impl.h
diff --git a/services/navigation/view_impl.h b/services/navigation/view_impl.h
index bec580b6f3c0c76b6122e2f09e4471262032e059..3319e760682e4bb18c761abe6414c6a5a429f96a 100644
--- a/services/navigation/view_impl.h
+++ b/services/navigation/view_impl.h
@@ -44,6 +44,8 @@ class ViewImpl : public mojom::View,
   void Stop() override;
   void GetWindowTreeClient(
       mus::mojom::WindowTreeClientRequest request) override;
+  void ShowInterstitial(const mojo::String& html) override;
+  void HideInterstitial() override;
 
   // content::WebContentsDelegate:
   void AddNewContents(content::WebContents* source,