Have the RequestCoordinator generate the offline_id

chrome/browser/android/offline_pages/prerendering_offliner.h

 // 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.
 
 #ifndef CHROME_BROWSER_ANDROID_OFFLINE_PAGES_PRERENDERING_OFFLINER_H_
 #define CHROME_BROWSER_ANDROID_OFFLINE_PAGES_PRERENDERING_OFFLINER_H_
 
 #include <memory>
 
 #include "base/android/application_status_listener.h"
@@ skipping 30 matching lines @@
   // Allows a loader to be injected for testing. This may only be done once
   // and must be called before any of the Offliner interface methods are called.
   void SetLoaderForTesting(std::unique_ptr<PrerenderingLoader> loader);
 
   void SetLowEndDeviceForTesting(bool is_low_end_device);
 
   void SetApplicationStateForTesting(
       base::android::ApplicationState application_state);
 
  protected:
-  // Internal method for requesting OfflinePageModel to save page.
-  // Exposed for unit testing.
+  // Internal method for requesting OfflinePageModel to save page.  Exposed for
+  // unit testing.  |proposed_offline_id| will be used if non-zero.  If it is
+  // zero, a new, random, id will be generated instead.
   // TODO(dougarnett): Consider making OfflinePageModel mockable instead.
   virtual void SavePage(const GURL& url,
                         const ClientId& client_id,
+                        int64_t proposed_offline_id,
                         std::unique_ptr<OfflinePageArchiver> archiver,
                         const SavePageCallback& save_callback);
 
  private:
   // Callback logic for PrerenderingLoader::LoadPage().
   void OnLoadPageDone(const SavePageRequest& request,
                       Offliner::RequestStatus load_status,
                       content::WebContents* web_contents);
 
   // Callback logic for OfflinePageModel::SavePage().
@@ skipping 23 matching lines @@
   // ApplicationStatusListener to monitor if the Chrome moves to the foreground.
   std::unique_ptr<base::android::ApplicationStatusListener> app_listener_;
   base::WeakPtrFactory<PrerenderingOffliner> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(PrerenderingOffliner);
 };
 
 }  // namespace offline_pages
 
 #endif  // CHROME_BROWSER_ANDROID_OFFLINE_PAGES_PRERENDERING_OFFLINER_H_