Revert "Move ExtensionCache to //extensions"

chrome/browser/extensions/updater/extension_cache_impl.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_impl.h"
 
 #include "base/bind.h"
 #include "base/memory/singleton.h"
 #include "base/metrics/histogram.h"
 #include "base/sequenced_task_runner.h"
@@ skipping 17 matching lines @@
 #endif// Directory where the extensions are cached.
 
 // Maximum size of local cache on disk.
 size_t kMaxCacheSize = 100 * 1024 * 1024;
 
 // Maximum age of unused extensions in cache.
 const int kMaxCacheAgeDays = 30;
 
 }  // namespace
 
+// static
+ExtensionCacheImpl* ExtensionCacheImpl::GetInstance() {
+  return Singleton<ExtensionCacheImpl>::get();
+}
+
 ExtensionCacheImpl::ExtensionCacheImpl()
   : cache_(new LocalExtensionCache(base::FilePath(kLocalCacheDir),
         kMaxCacheSize,
         base::TimeDelta::FromDays(kMaxCacheAgeDays),
         content::BrowserThread::GetBlockingPool()->
             GetSequencedTaskRunnerWithShutdownBehavior(
                 content::BrowserThread::GetBlockingPool()->GetSequenceToken(),
                 base::SequencedWorkerPool::SKIP_ON_SHUTDOWN))),
     weak_ptr_factory_(this) {
   notification_registrar_.Add(
@@ skipping 78 matching lines @@
       cache_->RemoveExtension(installer->expected_id());
       break;
     }
 
     default:
       NOTREACHED();
   }
 }
 
 }  // namespace extensions