Add a flag in WebAPK's proto when the Web App Manifest is no longer available.

chrome/browser/android/webapk/webapk.proto

 // 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.
 
 syntax = "proto2";
 
 option optimize_for = LITE_RUNTIME;
 
 package webapk;
 
@@ skipping 30 matching lines @@
 
   // Chrome's version.
   optional string requester_application_version = 6;
 
   // The Web App Manifest.
   optional WebAppManifest manifest = 7;
 
   // The cpu abi of the browser making the request.
   optional string android_abi = 8;
 
+  // If set true, this flag indicates that the Web App Manifest of the site is
+  // no longer available.
+  optional bool stale_manifest = 9;
+
   reserved 4;
 }
 
 // Contains data from the Web App Manifest.
 message WebAppManifest {
   optional string name = 1;
   optional string short_name = 2;
   optional string start_url = 4;
   repeated string scopes = 5;
   repeated Image icons = 6;
@@ skipping 12 matching lines @@
   // Murmur2 hash of the icon's bytes. There should not be any transformations
   // applied to the icon's bytes prior to taking the Murmur2 hash.
   optional string hash = 5;
 
   // Actual bytes of the image. This image may be re-encoded from the original
   // image and may not match the murmur2 hash field above.
   optional bytes image_data = 6;
 
   reserved 2 to 4;
 }