Disk Cache: Use the old WorkerPool for Async IO on iOS.

net/disk_cache/file.h

 // 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_FILE_H_
 #define NET_DISK_CACHE_FILE_H_
 
 #include "base/memory/ref_counted.h"
@@ skipping 52 matching lines @@
              FileIOCallback* callback, bool* completed);
 
   // Sets the file's length. The file is truncated or extended with zeros to
   // the new length.
   bool SetLength(size_t length);
   size_t GetLength();
 
   // Blocks until |num_pending_io| IO operations complete.
   static void WaitForPendingIO(int* num_pending_io);
 
+  // Drops current pending operations without waiting for them to complete.
+  static void DropPendingIO();
+
  protected:
   virtual ~File();
 
  private:
   // Performs the actual asynchronous write. If notify is set and there is no
   // callback, the call will be re-synchronized.
   bool AsyncWrite(const void* buffer, size_t buffer_len, size_t offset,
                   FileIOCallback* callback, bool* completed);
 
   // Infrastructure for async IO.
   int DoRead(void* buffer, size_t buffer_len, size_t offset);
   int DoWrite(const void* buffer, size_t buffer_len, size_t offset);
   void OnOperationComplete(FileIOCallback* callback, int result);
 
   bool init_;
   bool mixed_;
   base::PlatformFile platform_file_;  // Regular, asynchronous IO handle.
   base::PlatformFile sync_platform_file_;  // Synchronous IO handle.
 
   DISALLOW_COPY_AND_ASSIGN(File);
 };
 
 }  // namespace disk_cache
 
 #endif  // NET_DISK_CACHE_FILE_H_