[Offline Pages] Close race condition of multiple StartProcessing callers.

components/offline_pages/background/request_coordinator.h

 // 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.
 
 #ifndef COMPONENTS_OFFLINE_PAGES_BACKGROUND_REQUEST_COORDINATOR_H_
 #define COMPONENTS_OFFLINE_PAGES_BACKGROUND_REQUEST_COORDINATOR_H_
 
 #include <memory>
 
 #include "base/callback.h"
@@ skipping 128 matching lines @@
 
   // Returns the status of the most recent offlining.
   Offliner::RequestStatus last_offlining_status() {
     return last_offlining_status_;
   }
 
   bool is_busy() {
     return is_busy_;
   }
 
+  // Returns whether processing is starting (before it is decided to actually
+  // process a request (is_busy()) at this time or not.
+  bool is_starting() { return is_starting_; }
+
   // Tracks whether the last offlining attempt got canceled.  This is reset by
   // the next StartProcessing() call.
   bool is_canceled() {
     return is_stopped_;
   }
 
   OfflineEventLogger* GetLogger() {
     return &event_logger_;
   }
 
@@ skipping 82 matching lines @@
   void SetDeviceConditionsForTest(DeviceConditions& current_conditions) {
     current_conditions_.reset(new DeviceConditions(current_conditions));
   }
 
   friend class RequestCoordinatorTest;
 
   // The offliner can only handle one request at a time - if the offliner is
   // busy, prevent other requests.  This flag marks whether the offliner is in
   // use.
   bool is_busy_;
-  // True if the current request has been canceled.
+  // There is more than one path to start processing so this flag is used
+  // to avoid race conditions before is_busy_ is established.
+  bool is_starting_;
+  // True if the current processing window has been canceled.
   bool is_stopped_;
   // True if we should use the test connection type instead of the actual type.
   bool use_test_connection_type_;
   // For use by tests, a fake network connection type
   net::NetworkChangeNotifier::ConnectionType test_connection_type_;
   // Unowned pointer to the current offliner, if any.
   Offliner* offliner_;
   base::Time operation_start_time_;
   // The observers.
   base::ObserverList<Observer> observers_;
@@ skipping 23 matching lines @@
   base::TimeDelta offliner_timeout_;
   // Allows us to pass a weak pointer to callbacks.
   base::WeakPtrFactory<RequestCoordinator> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(RequestCoordinator);
 };
 
 }  // namespace offline_pages
 
 #endif  // COMPONENTS_OFFLINE_PAGES_BACKGROUND_REQUEST_COORDINATOR_H_