Fix losing of scoped feature channel in tests when it's equal to stable

extensions/common/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 EXTENSIONS_COMMON_FEATURES_FEATURE_CHANNEL_H_
 #define EXTENSIONS_COMMON_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.
+// need to come from an IPC. Note that the value set through this function may
+// be overridden by |ScopedCurrentChannel|.
 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.
+// Note that the lifetimes of multiple instances of this class must be disjoint
+// or nested, but never overlapping.
 class ScopedCurrentChannel {
  public:
   explicit ScopedCurrentChannel(version_info::Channel channel);
   ~ScopedCurrentChannel();
 
  private:
-  version_info::Channel original_channel_;
+  const version_info::Channel channel_;
+  const version_info::Channel original_overridden_channel_;
+  const int original_override_count_;
 
   DISALLOW_COPY_AND_ASSIGN(ScopedCurrentChannel);
 };
 
 }  // namespace extensions
 
 #endif  // EXTENSIONS_COMMON_FEATURES_FEATURE_CHANNEL_H_