[Offline Prefetch] Create a new JobScheduler task to wake up for net activity.

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 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,
     // but will not be used for deduplication.
     ClientId client_id;
 
     // This URL will be prefetched by the service.
     GURL url;
   };
 
+  // A |ScopedBackgroundTask| is created when we are running in a background
+  // task.  Destroying this object should notify the system that we are done
+  // processing the background task.
+  class ScopedBackgroundTask {
+   public:
+    ScopedBackgroundTask();
+    virtual ~ScopedBackgroundTask();
+
+    virtual void SetNeedsReschedule(bool reschedule) = 0;
+  };
+
   ~PrefetchService() override = default;
 
   // Called when a consumer has candidate URLs for the system to prefetch.
   // Duplicates are accepted by the PrefetchService but ignored.
   virtual void AddCandidatePrefetchURLs(
       const std::vector<PrefetchURL>& prefetch_urls) = 0;
 
   // Called when all existing suggestions are no longer considered valid for a
   // given namespace.  The prefetch service should remove any URLs that
   // have not yet started downloading within that namespace.
   virtual void RemoveAllUnprocessedPrefetchURLs(
       const std::string& name_space) = 0;
 
   // Called to invalidate a single PrefetchURL entry identified by |client_id|.
   // If multiple have the same |client_id|, they will all be removed.
   virtual void RemovePrefetchURLsByClientId(const ClientId& client_id) = 0;
+
+  virtual void BeginBackgroundTask(

[carlosk, 2017/04/19 23:01:38]

nit: add descriptive comment.

+      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;
 };
 
 }  // namespace offline_pages
 
 #endif  // COMPONENTS_OFFLINE_PAGES_CORE_PREFETCH_PREFETCH_SERVICE_IMPL_H_