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

net/disk_cache/storage_block-inl.h

Index: net/disk_cache/storage_block-inl.h
===================================================================
--- net/disk_cache/storage_block-inl.h	(revision 126788)
+++ net/disk_cache/storage_block-inl.h	(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.
 
@@ -89,6 +89,10 @@
   modified_ = true;
 }
 
+template<typename T> void StorageBlock<T>::clear_modified() {
+  modified_ = false;
+}
+
 template<typename T> T* StorageBlock<T>::Data() {
   if (!data_)
     AllocateData();