Add a general purpose facility for letting background tasks wait until

components/offline_pages/background/request_coordinator.cc

 // 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.
 
 #include "components/offline_pages/background/request_coordinator.h"
 
 #include <utility>
 
 #include "base/bind.h"
 #include "base/callback.h"
@@ skipping 51 matching lines @@
     RequestQueue::AddRequestResult result,
     const SavePageRequest& request) {
 
   // Inform the scheduler that we have an outstanding task.
   // TODO(petewil): Define proper TriggerConditions and set them.
   Scheduler::TriggerCondition conditions;
   scheduler_->Schedule(conditions);
 }
 
 void RequestCoordinator::RequestPicked(const SavePageRequest& request) {
-  Scheduler::TriggerCondition conditions;
-
-  // Ensure that the scheduler has actively scheduled a task.
-  scheduler_->Schedule(conditions);
-
   // Send the request on to the offliner.
   SendRequestToOffliner(request);
 }
 
 void RequestCoordinator::RequestQueueEmpty() {
   // TODO(petewil): return to the BackgroundScheduler by calling
   // ProcessingDoneCallback
 }
 
 bool RequestCoordinator::StartProcessing(
-    const base::Callback<void(bool)>& callback) {
+    base::Callback<void(bool)> callback) {
+  scheduler_callback_ = callback;
   // TODO(petewil): Check existing conditions (should be passed down from
   // BackgroundTask)
 
   // Choose a request to process that meets the available conditions.
   // This is an async call, and returns right away.
   picker_->ChooseNextRequest(
       base::Bind(&RequestCoordinator::RequestPicked,
                  weak_ptr_factory_.GetWeakPtr()),
       base::Bind(&RequestCoordinator::RequestQueueEmpty,
                  weak_ptr_factory_.GetWeakPtr()));
@@ skipping 23 matching lines @@
                                               Offliner::RequestStatus status) {
   DVLOG(2) << "offliner finished, saved: "
            << (status == Offliner::RequestStatus::SAVED) << ", "
            << __FUNCTION__;
   last_offlining_status_ = status;
 
   // TODO(petewil): Check time budget.  Start a request if we have time, return
   // to the scheduler if we are out of time.
 
   // TODO(petewil): If the request succeeded, remove it from the Queue.
+
+  // Return control to the scheduler when there is no more to do.
+  scheduler_callback_.Run(status == Offliner::RequestStatus::SAVED);
 }
 
 }  // namespace offline_pages