Revert "Move ExtensionCache to //extensions"

chrome/browser/extensions/updater/extension_cache_impl.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 CHROME_BROWSER_EXTENSIONS_UPDATER_EXTENSION_CACHE_IMPL_H_
 #define CHROME_BROWSER_EXTENSIONS_UPDATER_EXTENSION_CACHE_IMPL_H_
 
 #include <set>
 #include <string>
 #include <vector>
 
 #include "base/callback_forward.h"
 #include "base/files/file_path.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/memory/weak_ptr.h"
+#include "chrome/browser/extensions/updater/extension_cache.h"
 #include "content/public/browser/notification_observer.h"
 #include "content/public/browser/notification_registrar.h"
-#include "extensions/browser/updater/extension_cache.h"
 
 template <typename T> struct DefaultSingletonTraits;
 
 namespace extensions {
 
 class LocalExtensionCache;
 
 // Singleton call that caches extensions .crx files to share them between
 // multiple users and profiles on the machine.
 class ExtensionCacheImpl : public ExtensionCache,
                            public content::NotificationObserver {
  public:
-  ExtensionCacheImpl();
-  virtual ~ExtensionCacheImpl();
+  static ExtensionCacheImpl* GetInstance();
 
   // Implementation of ExtensionCache.
   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;
 
   // Implementation of content::NotificationObserver:
   virtual void Observe(int type,
                        const content::NotificationSource& source,
                        const content::NotificationDetails& details) override;
 
  private:
+  friend struct DefaultSingletonTraits<ExtensionCacheImpl>;
+
+  ExtensionCacheImpl();
+  virtual ~ExtensionCacheImpl();
+
   // Callback that is called when local cache is ready.
   void OnCacheInitialized();
 
   // Cache implementation that uses local cache dir.
   scoped_ptr<LocalExtensionCache> cache_;
 
   // Set of extensions that can be cached.
   std::set<std::string> allowed_extensions_;
 
   // List of callbacks that should be called when the cache is ready.
   std::vector<base::Closure> init_callbacks_;
 
   // Observes failures to install CRX files.
   content::NotificationRegistrar notification_registrar_;
 
   // Weak factory for callbacks.
   base::WeakPtrFactory<ExtensionCacheImpl> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(ExtensionCacheImpl);
 };
 
 }  // namespace extensions
 
 #endif  // CHROME_BROWSER_EXTENSIONS_UPDATER_EXTENSION_CACHE_IMPL_H_