Handle redirects in AuthenticatingURLLoaderImpl.

mojo/services/authenticating_url_loader/public/interfaces/authenticating_url_loader.mojom

 // Copyright 2014 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 mojo;
 
 import "network/public/interfaces/url_loader.mojom";
 
 interface AuthenticatingURLLoader {
   // Loads the given |request|, asynchronously producing |response|. If the
   // server indicates that authentication is needed, attempts to obtain an
   // OAuth2 token from the user and use that as authentication. Consult
   // |response| to determine if the request resulted in an error, was
   // redirected, or has a response body to be consumed.
   Start(URLRequest request) => (URLResponse response);
+
+  // If the request passed to |Start| had |auto_follow_redirects| set to false,
+  // then upon receiving an URLResponse with a non-NULL |redirect_url| field,
+  // |FollowRedirect| may be called to load the URL indicated by the redirect.
+  FollowRedirect() => (URLResponse response);
 };