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

chrome/browser/metrics/metrics_service.h

 // Copyright (c) 2011 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.
 
 // This file defines a service that collects information about the user
 // experience in order to help improve future versions of the app.
 
 #ifndef CHROME_BROWSER_METRICS_METRICS_SERVICE_H_
 #define CHROME_BROWSER_METRICS_METRICS_SERVICE_H_
 #pragma once
@@ skipping 72 matching lines @@
   // StartRecordingOnly starts the metrics recording but not reporting, for use
   // in tests only.
   void Start();
   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();
 
+  // 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);
 
   // Set up notifications which indicate that a user is performing work. This is
   // useful to allow some features to sleep, until the machine becomes active,
   // such as precluding UMA uploads unless there was recent activity.
   static void SetUpNotifications(NotificationRegistrar* registrar,
                                  NotificationObserver* observer);
 
@@ skipping 328 matching lines @@
   FRIEND_TEST_ALL_PREFIXES(MetricsServiceTest, CorruptSizeOfLogList);
   FRIEND_TEST_ALL_PREFIXES(MetricsServiceTest, CorruptChecksumOfLogList);
   FRIEND_TEST_ALL_PREFIXES(MetricsServiceTest, ClientIdGeneratesAllZeroes);
   FRIEND_TEST_ALL_PREFIXES(MetricsServiceTest, ClientIdGeneratesCorrectly);
   FRIEND_TEST_ALL_PREFIXES(MetricsServiceTest, ClientIdCorrectlyFormatted);
 
   DISALLOW_COPY_AND_ASSIGN(MetricsService);
 };
 
 #endif  // CHROME_BROWSER_METRICS_METRICS_SERVICE_H_