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

chrome/common/extensions/features/feature.cc

Index: chrome/common/extensions/features/feature.cc
diff --git a/chrome/common/extensions/features/feature.cc b/chrome/common/extensions/features/feature.cc
index 3da8726e386acf3003ece3a22741e6612cb42836..275c807aabd39fe6b75e85b114387e3e9637cf04 100644
--- a/chrome/common/extensions/features/feature.cc
+++ b/chrome/common/extensions/features/feature.cc
@@ -246,9 +246,11 @@ std::string Feature::GetErrorMessage(Feature::Availability result) {
           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 "";