Handle redirects in AuthenticatingURLLoaderImpl.

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

Index: mojo/services/authenticating_url_loader/public/interfaces/authenticating_url_loader.mojom
diff --git a/mojo/services/authenticating_url_loader/public/interfaces/authenticating_url_loader.mojom b/mojo/services/authenticating_url_loader/public/interfaces/authenticating_url_loader.mojom
index 4fff367aeb8b37abba526f4fbf15a172ea1f7d8a..b73c919f69652d5c68dfa90bc85bdbfb0b5befd0 100644
--- a/mojo/services/authenticating_url_loader/public/interfaces/authenticating_url_loader.mojom
+++ b/mojo/services/authenticating_url_loader/public/interfaces/authenticating_url_loader.mojom
@@ -13,4 +13,9 @@ interface AuthenticatingURLLoader {
   // |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);
 };