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

components/offline_pages/core/prefetch/prefetch_service.h

Index: components/offline_pages/core/prefetch/prefetch_service.h
diff --git a/components/offline_pages/core/prefetch/prefetch_service.h b/components/offline_pages/core/prefetch/prefetch_service.h
index 0bb85086e858397bff3ef9d02bcca313993ce0ea..eee0de0b14d110023c014e66d4b6967a409ff6b7 100644
--- a/components/offline_pages/core/prefetch/prefetch_service.h
+++ b/components/offline_pages/core/prefetch/prefetch_service.h
@@ -27,6 +27,17 @@ class PrefetchService : public KeyedService {
     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.
@@ -43,6 +54,14 @@ class PrefetchService : public KeyedService {
   // 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