Set up a backup schedule request if we have deferred requests.

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 9bb828867fd07cb7d98df95eeb2b81c87fec3d45..092d608799793ffb6732476403decf05fc5a5ae4 100644
--- a/components/offline_pages/background/request_coordinator.cc
+++ b/components/offline_pages/background/request_coordinator.cc
@@ -25,6 +25,7 @@ namespace offline_pages {
 
 namespace {
 const bool kUserRequest = true;
+const int kDisabledTaskRecheckSeconds = 5 * 60;

[Dmitry Titov, 2016/10/10 17:29:45]

I think this needs to be a much shorter interval. Here is the logic:
- these tasks will be there only while disabled_requests_ is not empty, if it
becomes empty we'll clear them right away.
- that list will only be non-empty while Chrome is running and actively
snapshotting page(s) in tabs
- it's good for user if we keep download 'running' even if they switch to other
app.

So lets say we have this period to be 5 seconds. While Chrome is running,
responding to a once-in-5-seconds task is very cheap. Once Chrome is evicted
from RAM, the next wake up will be the last of those, and it'll run background
loader 'in parallel' with whatever activity is there - same as it may do in 5
minutes, but with better match of user expectations.

WDYT?

[Pete Williamson, 2016/10/10 19:45:17]

Done.

 
 // Records the final request status UMA for an offlining request. This should
 // only be called once per Offliner::LoadAndSave request.
@@ -460,8 +461,15 @@ void RequestCoordinator::RequestNotPicked(
   // Clear the outstanding "safety" task in the scheduler.
   scheduler_->Unschedule();
 
-  if (non_user_requested_tasks_remaining)
+  // If disabled tasks remain, post a new safety task for 5 min from now.
+  if (disabled_requests_.size() > 0) {
+    scheduler_->BackupSchedule(GetTriggerConditions(kUserRequest),
+                               kDisabledTaskRecheckSeconds);
+  } else if (non_user_requested_tasks_remaining) {
+    // If we don't have any of those, check for non-user-requested tasks.
     scheduler_->Schedule(GetTriggerConditions(!kUserRequest));
+  }
+
   // Let the scheduler know we are done processing.
   scheduler_callback_.Run(true);
 }
@@ -583,9 +591,13 @@ void RequestCoordinator::OfflinerDoneCallback(const SavePageRequest& request,
 
 void RequestCoordinator::EnableForOffliner(int64_t request_id) {
     disabled_requests_.erase(request_id);
+    // If we are not busy, start processing right away.
+    StartProcessingIfConnected();
 }
 
-void RequestCoordinator::MarkRequestCompleted(int64_t request_id) {}
+void RequestCoordinator::MarkRequestCompleted(int64_t request_id) {
+  // TODO: Remove the request, but send out SUCCEEDED instead of removed.
+}
 
 const Scheduler::TriggerConditions RequestCoordinator::GetTriggerConditions(
     const bool user_requested) {