Add a general purpose facility for letting background tasks wait until

components/offline_pages/background/request_coordinator.cc

Index: components/offline_pages/background/request_coordinator.cc
diff --git a/components/offline_pages/background/request_coordinator.cc b/components/offline_pages/background/request_coordinator.cc
index 0a0ebdb23c01345f3a6a8547ce4dd4213c6f98de..532725cc87cf3055f6e3f679c2b2e45fbb4b0206 100644
--- a/components/offline_pages/background/request_coordinator.cc
+++ b/components/offline_pages/background/request_coordinator.cc
@@ -69,11 +69,6 @@ void RequestCoordinator::AddRequestResultCallback(
 }
 
 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);
 }
@@ -84,7 +79,8 @@ void RequestCoordinator::RequestQueueEmpty() {
 }
 
 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)
 
@@ -128,6 +124,9 @@ void RequestCoordinator::OfflinerDoneCallback(const SavePageRequest& request,
   // 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