Revert "Move ExtensionCache to //extensions"

chrome/browser/extensions/updater/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_EXTENSION_CACHE_H_
-#define EXTENSIONS_BROWSER_UPDATER_EXTENSION_CACHE_H_
+#ifndef CHROME_BROWSER_EXTENSIONS_UPDATER_EXTENSION_CACHE_H_
+#define CHROME_BROWSER_EXTENSIONS_UPDATER_EXTENSION_CACHE_H_
 
 #include <string>
 
 #include "base/callback_forward.h"
 #include "base/files/file_path.h"
 
 namespace extensions {
 
 // ExtensionCache interface that caches extensions .crx files to share them
 // between multiple users and profiles on the machine.
 class ExtensionCache {
  public:
+  // Return global singleton instance of ExtensionCache.
+  static ExtensionCache* GetInstance();
+
   // Callback that is invoked when the file placed when PutExtension done.
   typedef base::Callback<void(const base::FilePath& file_path,
                               bool file_ownership_passed)> PutExtensionCallback;
 
-  ExtensionCache() {}
-  virtual ~ExtensionCache() {}
-
   // Initialize cache in background. The |callback| is called when cache ready.
   // Can be called multiple times. The |callback| can be called immediately if
   // cache is ready.
   virtual void Start(const base::Closure& callback) = 0;
 
   // Shut down the cache. Must be called at most once on browser shutdown.
   virtual void Shutdown(const base::Closure& callback) = 0;
 
   // Allow caching for the extension with given |id|. User specific extensions
   // should not be cached for privacy reasons. But default apps including policy
@@ skipping 11 matching lines @@
   // the cache will removed be on next run so it can be safely used. Extension
   // will be marked as used with current timestamp. The file will be available
   // via GetExtension when |callback| is called. Original |file_path| won't be
   // deleted from the disk. There is no guarantee that |callback| will be
   // called.
   virtual void PutExtension(const std::string& id,
                             const base::FilePath& file_path,
                             const std::string& version,
                             const PutExtensionCallback& callback) = 0;
 
- private:
-  DISALLOW_COPY_AND_ASSIGN(ExtensionCache);
+ protected:
+  virtual ~ExtensionCache() {}
+
+  // Sets the singleton to the given |cache|. Returns the previous value of
+  // the singleton. Ownership is not transferred.
+  static ExtensionCache* SetForTesting(ExtensionCache* cache);
 };
 
 }  // namespace extensions
 
-#endif  // EXTENSIONS_BROWSER_UPDATER_EXTENSION_CACHE_H_
+#endif  // CHROME_BROWSER_EXTENSIONS_UPDATER_EXTENSION_CACHE_H_