Add one-time randomization support for FieldTrial, and the ability to

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 491a375999b1d495c654b82972b4d48252e0e55e..9809934ff815fee014faf82827d31e71437d65df 100644
--- a/chrome/browser/metrics/metrics_service.h
+++ b/chrome/browser/metrics/metrics_service.h
@@ -82,6 +82,10 @@ class MetricsService : public NotificationObserver,
   void StartRecordingOnly();
   void Stop();
 
+  // Returns the client ID for this client, or the empty string if metrics
+  // recording is not currently running.
+  std::string GetClientId();
+
   // 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);