[BackgroundSync] Handle storage failure

content/browser/cache_storage/cache_storage_scheduler.h

 // Copyright 2015 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 CONTENT_BROWSER_CACHE_STORAGE_CACHE_STORAGE_SCHEDULER_H_
 #define CONTENT_BROWSER_CACHE_STORAGE_CACHE_STORAGE_SCHEDULER_H_
 
 #include <list>
 
 #include "base/callback.h"
 #include "content/common/content_export.h"
 
 namespace content {
 
+// TODO(jkarlin): Support readers and writers so operations can run in parallel.
+// TODO(jkarlin): Support operation identification so that ops can be checked in
+// DCHECKs.
+
+// CacheStorageScheduler runs the scheduled callbacks sequentially. Add an
+// operation by calling ScheduleOperation() with your callback. Once your
+// operation is done be sure to call CompleteOperationAndRunNext() to schedule
+// the next operation.
 class CONTENT_EXPORT CacheStorageScheduler {
  public:
   CacheStorageScheduler();
   virtual ~CacheStorageScheduler();
 
   // Adds the operation to the tail of the queue and starts it if the scheduler
   // is idle.
   void ScheduleOperation(const base::Closure& closure);
 
   // Call this after each operation completes. It cleans up the current
   // operation and starts the next.
   void CompleteOperationAndRunNext();
 
   // Returns true if there are any running or pending operations.
   bool ScheduledOperations() const;
 
  private:
   void RunOperationIfIdle();
 
   // The list of operations waiting on initialization.
   std::list<base::Closure> pending_operations_;
   bool operation_running_;
 
   DISALLOW_COPY_AND_ASSIGN(CacheStorageScheduler);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_CACHE_STORAGE_CACHE_STORAGE_SCHEDULER_H_