Log the channel that we're on when failing due to unsupported features, to aid in debugging.

chrome/common/extensions/features/feature.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/common/extensions/features/feature.h"
 
 #include <map>
 
 #include "base/command_line.h"
 #include "base/lazy_instance.h"
@@ skipping 228 matching lines @@
       return base::StringPrintf(
           "'%s' requires manifest version of %d or lower.",
           name().c_str(),
           max_manifest_version_);
     case NOT_PRESENT:
       return base::StringPrintf(
           "'%s' requires a different Feature that is not present.",
           name().c_str());
     case UNSUPPORTED_CHANNEL:
       return base::StringPrintf(
-          "'%s' requires Google Chrome %s channel or newer.",
+          "'%s' requires Google Chrome %s channel or newer, and we're running "
+              "on the %s channel.",
           name().c_str(),
-          GetChannelName(channel_).c_str());
+          GetChannelName(channel_).c_str(),
+          GetChannelName(GetCurrentChannel()).c_str());
   }
 
   return "";
 }
 
 Feature::Availability Feature::IsAvailableToManifest(
     const std::string& extension_id,
     Extension::Type type,
     Location location,
     int manifest_version,
@@ skipping 66 matching lines @@
 chrome::VersionInfo::Channel Feature::GetCurrentChannel() {
   return g_current_channel;
 }
 
 // static
 void Feature::SetCurrentChannel(VersionInfo::Channel channel) {
   g_current_channel = channel;
 }
 
 }  // namespace