[Offline Pages] Add a GCMAppHandler for offline page prefetch.

components/offline_pages/core/prefetch/prefetch_service.h

 // Copyright 2017 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 COMPONENTS_OFFLINE_PAGES_CORE_PREFETCH_PREFETCH_SERVICE_H_
 #define COMPONENTS_OFFLINE_PAGES_CORE_PREFETCH_PREFETCH_SERVICE_H_
 
 #include "components/keyed_service/core/keyed_service.h"
 #include "components/offline_pages/core/offline_page_item.h"
 
 class GURL;
 
+namespace gcm {
+class GCMDriver;
+}
+
 namespace offline_pages {
 
 // Main class for the Offline Pages Prefetching feature, which will ask a server
 // to package content from interesting URLs and send it to Chrome for
 // consumption while offline.
 class PrefetchService : public KeyedService {
  public:
   struct PrefetchURL {
     // Used to differentiate URLs from different sources.  |name_space| should
     // be unique per source. |id| can be anything useful to identify the page,
@@ skipping 37 matching lines @@
   // Called when Android OS has scheduled us for background work.  When
   // destroyed, |task| will call back and inform the OS that we are done work
   // (if required).  |task| also manages rescheduling behavior.
   virtual void BeginBackgroundTask(
       std::unique_ptr<ScopedBackgroundTask> task) = 0;
 
   // Called when a task must stop immediately due to system constraints. After
   // this call completes, the system will reschedule the task based on whether
   // SetNeedsReschedule has been called.
   virtual void StopBackgroundTask(ScopedBackgroundTask* task) = 0;
+
+  // When GCMDriver starts up, this method is called so that we can listen for
+  // messages corresponding to our app ID.
+  virtual void RegisterWithGCMDriver(gcm::GCMDriver* driver) = 0;
 };
 
 }  // namespace offline_pages
 
 #endif  // COMPONENTS_OFFLINE_PAGES_CORE_PREFETCH_PREFETCH_SERVICE_IMPL_H_