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

net/disk_cache/file_win.cc

Index: net/disk_cache/file_win.cc
===================================================================
--- net/disk_cache/file_win.cc	(revision 126788)
+++ net/disk_cache/file_win.cc	(working copy)
@@ -1,4 +1,4 @@
-// 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.
 
@@ -264,4 +264,9 @@
   }
 }
 
+// Static.
+void File::DropPendingIO() {
+  // Nothing to do here.
+}
+
 }  // namespace disk_cache