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

chrome/browser/browser_main.cc

 // 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.
 
 #include "chrome/browser/browser_main.h"
 
 #include <algorithm>
 #include <string>
 #include <vector>
 
@@ skipping 255 matching lines @@
 // This will be called after the command-line has been mutated by about:flags
 MetricsService* BrowserMainParts::SetupMetricsAndFieldTrials(
     const CommandLine& parsed_command_line,
     PrefService* local_state) {
   // Must initialize metrics after labs have been converted into switches,
   // but before field trials are set up (so that client ID is available for
   // one-time randomized field trials).
   MetricsService* metrics = InitializeMetrics(parsed_command_line, local_state);
 
   // Initialize FieldTrialList to support FieldTrials that use one-time
-  // randomization. The client ID will be empty if the user has not opted
-  // to send metrics.
-  field_trial_list_.reset(new base::FieldTrialList(metrics->GetClientId()));
+  // randomization. The client ID will not be empty even if the user has not

[jar (doing other things), 2011/07/18 17:33:49]

This appears problematic from a privacy perspective... if I understand the
comment.

We had a lot of feedback from privacy groups indicating that we absolutely
should NOT tag a user with a unique ID if we are not going to send data via UMA.
 At one point, a special non-Google version of Chromium started to become
popular with its central "feature" being that it trashed this value.

Bottom line: If the user opts out of the UMA upload, we don't want to set a
persistent tag in the profile.  Yes, it is true, that we won't use it.... but it
is considered undesirable.

+  // opted to send metrics.
+  field_trial_list_.reset(
+      new base::FieldTrialList(metrics->GetClientIdNonEmpty()));
 
   SetupFieldTrials(metrics->recording_active(),
                    local_state->IsManagedPreference(
                        prefs::kMaxConnectionsPerProxy));
 
   // Initialize FieldTrialSynchronizer system. This is a singleton and is used
   // for posting tasks via NewRunnableMethod. Its deleted when it goes out of
   // scope. Even though NewRunnableMethod does AddRef and Release, the object
   // will not be deleted after the Task is executed.
   field_trial_synchronizer_ = new FieldTrialSynchronizer();
@@ skipping 1797 matching lines @@
 #if defined(OS_CHROMEOS)
   // To be precise, logout (browser shutdown) is not yet done, but the
   // remaining work is negligible, hence we say LogoutDone here.
   chromeos::BootTimesLoader::Get()->AddLogoutTimeMarker("LogoutDone",
                                                         false);
   chromeos::BootTimesLoader::Get()->WriteLogoutTimes();
 #endif
   TRACE_EVENT_END_ETW("BrowserMain", 0, 0);
   return result_code;
 }