Revert "Move ExtensionCache to //extensions"

chrome/browser/extensions/updater/extension_cache_fake.cc

 // 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.
 
 #include "chrome/browser/extensions/updater/extension_cache_fake.h"
 
 #include "base/bind.h"
 #include "base/stl_util.h"
 #include "content/public/browser/browser_thread.h"
 
 namespace extensions {
 
 ExtensionCacheFake::ExtensionCacheFake() {
+  ExtensionCache::SetForTesting(this);
 }
 
 ExtensionCacheFake::~ExtensionCacheFake() {
+  ExtensionCache::SetForTesting(NULL);
 }
 
 void ExtensionCacheFake::Start(const base::Closure& callback) {
   content::BrowserThread::PostTask(
       content::BrowserThread::UI,
       FROM_HERE,
       callback);
 }
 
 void ExtensionCacheFake::Shutdown(const base::Closure& callback) {
@@ skipping 32 matching lines @@
     content::BrowserThread::PostTask(
         content::BrowserThread::UI,
         FROM_HERE,
         base::Bind(callback, file_path, false));
   } else {
     callback.Run(file_path, true);
   }
 }
 
 }  // namespace extensions