[Offlining] Updates the tab helper to use the async OfflinePageModel API

chrome/browser/android/webapps/add_to_homescreen_data_fetcher.cc

 // Copyright 2015 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.
 
 #include "chrome/browser/android/webapps/add_to_homescreen_data_fetcher.h"
 
 #include "base/bind.h"
 #include "base/callback.h"
 #include "base/location.h"
 #include "base/strings/string16.h"
@@ skipping 253 matching lines @@
   shortcut_info_.is_icon_generated = is_generated;
   is_ready_ = true;
   weak_observer_->OnDataAvailable(shortcut_info_, shortcut_icon_);
 }
 
 GURL AddToHomescreenDataFetcher::GetShortcutUrl(const GURL& actual_url) {
   GURL original_url =
       dom_distiller::url_utils::GetOriginalUrlFromDistillerUrl(actual_url);
 
   // If URL points to an offline content, get original URL.
-  GURL online_url = offline_pages::OfflinePageUtils::GetOnlineURLForOfflineURL(
-      web_contents()->GetBrowserContext(), original_url);
+  GURL online_url =
+      offline_pages::OfflinePageUtils::MaybeGetOnlineURLForOfflineURL(
+          web_contents()->GetBrowserContext(), original_url);
   if (online_url.is_valid())
     return online_url;
 
   return original_url;
 }