[Extensions] Move Feature channel code into //extensions

chrome/common/extensions/features/feature_channel.h

-// Copyright 2013 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_COMMON_EXTENSIONS_FEATURES_FEATURE_CHANNEL_H_
-#define CHROME_COMMON_EXTENSIONS_FEATURES_FEATURE_CHANNEL_H_
-
-#include "base/macros.h"
-
-namespace version_info {
-enum class Channel;
-}
-
-namespace extensions {
-
-// Gets the current channel as seen by the Feature system.
-version_info::Channel GetCurrentChannel();
-
-// Sets the current channel as seen by the Feature system. In the browser
-// process this should be chrome::GetChannel(), and in the renderer this will
-// need to come from an IPC.
-void SetCurrentChannel(version_info::Channel channel);
-
-// Gets the default channel as seen by the Feature system.
-version_info::Channel GetDefaultChannel();
-
-// Scoped channel setter. Use for tests.
-class ScopedCurrentChannel {
- public:
-  explicit ScopedCurrentChannel(version_info::Channel channel);
-  ~ScopedCurrentChannel();
-
- private:
-  version_info::Channel original_channel_;
-
-  DISALLOW_COPY_AND_ASSIGN(ScopedCurrentChannel);
-};
-
-}  // namespace extensions
-
-#endif  // CHROME_COMMON_EXTENSIONS_FEATURES_FEATURE_CHANNEL_H_