Only set the channel from ExtensionSystem if there hasn't been one set already.

chrome/browser/extensions/extension_system.cc

 // Copyright (c) 2012 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/extension_system.h"
 
 #include "base/bind.h"
 #include "base/command_line.h"
 #include "base/file_path.h"
 #include "base/string_tokenizer.h"
@@ skipping 33 matching lines @@
 
 using content::BrowserThread;
 
 namespace extensions {
 
 //
 // ExtensionSystem
 //
 
 ExtensionSystem::ExtensionSystem() {
-  Feature::SetCurrentChannel(chrome::VersionInfo::GetChannel());
+  // Only set if it hasn't already been set (e.g. by a test).
+  if (Feature::GetCurrentChannel() == Feature::GetDefaultChannel())
+    Feature::SetCurrentChannel(chrome::VersionInfo::GetChannel());
 }
 
 ExtensionSystem::~ExtensionSystem() {
 }
 
 // static
 ExtensionSystem* ExtensionSystem::Get(Profile* profile) {
   return ExtensionSystemFactory::GetForProfile(profile);
 }
 
@@ skipping 309 matching lines @@
 void ExtensionSystemImpl::UnregisterExtensionWithRequestContexts(
     const std::string& extension_id,
     const extension_misc::UnloadedExtensionReason reason) {
   BrowserThread::PostTask(
       BrowserThread::IO, FROM_HERE,
       base::Bind(&ExtensionInfoMap::RemoveExtension, info_map(),
                  extension_id, reason));
 }
 
 }  // namespace extensions