Remove base::NonThreadSafe now that all users are gone!!

storage/browser/quota/usage_tracker.h

 // Copyright 2013 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 STORAGE_BROWSER_QUOTA_USAGE_TRACKER_H_
 #define STORAGE_BROWSER_QUOTA_USAGE_TRACKER_H_
 
 #include <stdint.h>
 
 #include <map>
 #include <memory>
 #include <set>
 #include <string>
 
 #include "base/callback.h"
 #include "base/macros.h"
-#include "base/threading/non_thread_safe.h"
 #include "storage/browser/quota/quota_callbacks.h"
 #include "storage/browser/quota/quota_client.h"
 #include "storage/browser/quota/quota_task.h"
 #include "storage/browser/quota/special_storage_policy.h"
 #include "storage/browser/storage_browser_export.h"
 #include "storage/common/quota/quota_types.h"
 #include "url/gurl.h"
 
 namespace storage {
 
@@ skipping 66 matching lines @@
 
   StorageMonitor* storage_monitor_;
 
   base::WeakPtrFactory<UsageTracker> weak_factory_;
   DISALLOW_COPY_AND_ASSIGN(UsageTracker);
 };
 
 }  // namespace storage
 
 #endif  // STORAGE_BROWSER_QUOTA_USAGE_TRACKER_H_