Add a switch for faking channels for Variations filtering.

chrome/browser/metrics/variations/variations_service.h

Index: chrome/browser/metrics/variations/variations_service.h
diff --git a/chrome/browser/metrics/variations/variations_service.h b/chrome/browser/metrics/variations/variations_service.h
index 5a363874deafeb12d1c1abf36b7811bc7c3052de..1b2cca3717447c924e427c57876a0abce61a9851 100644
--- a/chrome/browser/metrics/variations/variations_service.h
+++ b/chrome/browser/metrics/variations/variations_service.h
@@ -93,6 +93,13 @@ class VariationsService
                      const base::Time& seed_date,
                      PrefService* local_prefs);
 
+  // Wrapper around channel checking, used to enable channel mocking for
+  // testing. If the current browser channel is not UNKNOWN, this will return
+  // that channel value. Otherwise, if the fake channel flag is provided, this
+  // will return the fake channel. Failing that, this will return the UNKNOWN
+  // channel.
+  static chrome::VersionInfo::Channel GetChannelForVariations();
+
   // Returns whether |study| should be disabled according to its restriction
   // parameters. Uses |version_info| for min / max version checks and
   // |reference_date| for the start date check.