Revert "Move ExtensionCache to //extensions"

extensions/browser/updater/null_extension_cache.h

-// Copyright 2014 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 EXTENSIONS_BROWSER_UPDATER_NULL_EXTENSION_CACHE_H_
-#define EXTENSIONS_BROWSER_UPDATER_NULL_EXTENSION_CACHE_H_
-
-#include "extensions/browser/updater/extension_cache.h"
-
-namespace extensions {
-
-// Implements a pass-thru (i.e. do-nothing) ExtensionCache.
-class NullExtensionCache : public ExtensionCache {
- public:
-  NullExtensionCache();
-  virtual ~NullExtensionCache();
-
-  // ExtensionCache implementation.
-  virtual void Start(const base::Closure& callback) override;
-  virtual void Shutdown(const base::Closure& callback) override;
-  virtual void AllowCaching(const std::string& id) override;
-  virtual bool GetExtension(const std::string& id,
-                            base::FilePath* file_path,
-                            std::string* version) override;
-  virtual void PutExtension(const std::string& id,
-                            const base::FilePath& file_path,
-                            const std::string& version,
-                            const PutExtensionCallback& callback) override;
-
- private:
-  DISALLOW_COPY_AND_ASSIGN(NullExtensionCache);
-};
-
-}  // namespace extensions
-
-#endif  // EXTENSIONS_BROWSER_UPDATER_NULL_EXTENSION_CACHE_H_