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

services/navigation/public/interfaces/view.mojom

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 module navigation.mojom;
 
 import "components/mus/public/interfaces/window_tree.mojom";
 import "ui/gfx/geometry/mojo/geometry.mojom";
 import "url/mojo/url.mojom";
 
@@ skipping 21 matching lines @@
   NavigateTo(url.mojom.Url url);
 
   GoBack();
   GoForward();
   Reload(bool skip_cache);
   Stop();
 
   // Obtains a Mus WindowTreeClient for the View, so it can be embedded in a
   // UI.
   GetWindowTreeClient(mus.mojom.WindowTreeClient& client);
+
+  ShowInterstitial(string html);
+  HideInterstitial();
 };