Disk cache: Remove all non essential synchronization from the cache destructor.

net/disk_cache/backend_impl.h

-// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// Copyright (c) 2012 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.
 
 // See net/disk_cache/disk_cache.h for the public interface of the cache.
 
 #ifndef NET_DISK_CACHE_BACKEND_IMPL_H_
 #define NET_DISK_CACHE_BACKEND_IMPL_H_
 #pragma once
 
 #include "base/file_path.h"
@@ skipping 81 matching lines @@
 
   // Sets the cache type for this backend.
   void SetType(net::CacheType type);
 
   // Returns the full name for an external storage file.
   FilePath GetFileName(Addr address) const;
 
   // Returns the actual file used to store a given (non-external) address.
   MappedFile* File(Addr address);
 
-  InFlightBackendIO* background_queue() {
-    return &background_queue_;
-  }
+  // Returns a weak pointer to the background queue.
+  base::WeakPtr<InFlightBackendIO> GetBackgroundQueue();
 
   // Creates an external storage file.
   bool CreateExternalFile(Addr* address);
 
   // Creates a new storage block of size block_count.
   bool CreateBlock(FileType block_type, int block_count,
                    Addr* block_address);
 
   // Deletes a given storage block. deep set to true can be used to zero-fill
   // the related storage in addition of releasing the related block.
@@ skipping 277 matching lines @@
 
   DISALLOW_COPY_AND_ASSIGN(BackendImpl);
 };
 
 // Returns the preferred max cache size given the available disk space.
 NET_EXPORT_PRIVATE int PreferedCacheSize(int64 available);
 
 }  // namespace disk_cache
 
 #endif  // NET_DISK_CACHE_BACKEND_IMPL_H_