Improve the page download:

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 620 matching lines @@
       // No further processing in this service window.
       break;
     default:
       // Make explicit choice about new status codes that actually reach here.
       // Their default is no further processing in this service window.
       NOTREACHED();
   }
 }
 
 void RequestCoordinator::EnableForOffliner(int64_t request_id) {
-    disabled_requests_.erase(request_id);
-    // If we are not busy, start processing right away.
-    StartProcessingIfConnected();
+  if (disabled_requests_.find(request_id) == disabled_requests_.end())

[dewittj, 2016/10/12 03:27:27]

this is a subtle difference and not covered by any tests; what is the point of
this change?

[Pete Williamson, 2016/10/12 17:33:36]

Agree with DewittJ that a comment here would help.

Suggest (both here and below)
// Since the recent tab helper might call multiple times, ignore subsequent
calls for a particular request_id.

[Dmitry Titov, 2016/10/12 23:11:14]

Done. Added comment. Peter, could you consider adding a test?

[Pete Williamson, 2016/10/12 23:31:41]

Sure.  Open bug?

+    return;
+  disabled_requests_.erase(request_id);
+  // If we are not busy, start processing right away.
+  StartProcessingIfConnected();
 }
 
 void RequestCoordinator::MarkRequestCompleted(int64_t request_id) {
+  if (disabled_requests_.find(request_id) == disabled_requests_.end())
+    return;
+  disabled_requests_.erase(request_id);
+
   // Remove the request, but send out SUCCEEDED instead of removed.
   std::vector<int64_t> request_ids { request_id };
     queue_->RemoveRequests(
       request_ids,
       base::Bind(&RequestCoordinator::HandleRemovedRequestsAndCallback,
                  weak_ptr_factory_.GetWeakPtr(),
                  base::Bind(&RequestCoordinator::CompletedRequestCallback,
                             weak_ptr_factory_.GetWeakPtr()),
                  BackgroundSavePageResult::SUCCESS));
 }
@@ skipping 36 matching lines @@
 
 ClientPolicyController* RequestCoordinator::GetPolicyController() {
   return policy_controller_.get();
 }
 
 void RequestCoordinator::Shutdown() {
   network_quality_estimator_ = nullptr;
 }
 
 }  // namespace offline_pages