Allow one-time randomization in field trials to work even if metrics are disabled.

chrome/browser/metrics/metrics_service.h

Index: chrome/browser/metrics/metrics_service.h
diff --git a/chrome/browser/metrics/metrics_service.h b/chrome/browser/metrics/metrics_service.h
index 24e143b454914b3e0c25ed94105afd0b4aa43384..7d7bc2a43c7f3b22f8f6b05e6bab314a7cc19985 100644
--- a/chrome/browser/metrics/metrics_service.h
+++ b/chrome/browser/metrics/metrics_service.h
@@ -90,6 +90,10 @@ class MetricsService : public NotificationObserver,
   // recording is not currently running.
   std::string GetClientId();
 
+  // Returns the client ID for this client. It will be non-empty, even if
+  // metrics recording is not currently running.
+  std::string GetClientIdNonEmpty();
+
   // At startup, prefs needs to be called with a list of all the pref names and
   // types we'll be using.
   static void RegisterPrefs(PrefService* local_state);