Add an API to Pause and Resume background offlining requests.

components/offline_pages/background/request_queue_store_sql.h

Index: components/offline_pages/background/request_queue_store_sql.h
diff --git a/components/offline_pages/background/request_queue_store_sql.h b/components/offline_pages/background/request_queue_store_sql.h
index 18f6e8792d85715384c7291adfc60cf67944d2db..67ff36fdd348a9fed01a3a23e925c96711b76590 100644
--- a/components/offline_pages/background/request_queue_store_sql.h
+++ b/components/offline_pages/background/request_queue_store_sql.h
@@ -40,6 +40,10 @@ class RequestQueueStoreSQL : public RequestQueueStore {
                       const RemoveCallback& callback) override;
   void RemoveRequestsByClientId(const std::vector<ClientId>& client_ids,
                                 const RemoveCallback& callback) override;
+  void ChangeRequestsState(const std::vector<int64_t>& request_ids,
+                           const SavePageRequest::RequestState new_state,
+                           const UpdateCallback& callback) override;
+
   void Reset(const ResetCallback& callback) override;
 
  private:
@@ -66,11 +70,20 @@ class RequestQueueStoreSQL : public RequestQueueStore {
       scoped_refptr<base::SingleThreadTaskRunner> runner,
       const std::vector<ClientId>& client_ids,
       const RemoveCallback& callback);
+  static void ChangeRequestsStateSync(
+      sql::Connection* db,
+      scoped_refptr<base::SingleThreadTaskRunner> runner,
+      const std::vector<int64_t>& request_ids,
+      const SavePageRequest::RequestState new_state,
+      const UpdateCallback& callback);
   static void ResetSync(sql::Connection* db,
                         const base::FilePath& db_file_path,
                         scoped_refptr<base::SingleThreadTaskRunner> runner,
                         const ResetCallback& callback);
 
+  // Helper functions to return immediately if no database is found.
+  bool CheckDb(const base::Closure& callback);
+
   // Used to initialize DB connection.
   static void OpenConnectionSync(
       sql::Connection* db,