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

chrome/browser/browser_main.cc

Index: chrome/browser/browser_main.cc
diff --git a/chrome/browser/browser_main.cc b/chrome/browser/browser_main.cc
index 5c10233a0518c1bfa5713bd53f257ffa2cb9cf01..e742ca0a3fcde6dd2d59680a48ddcd84d28efdc7 100644
--- a/chrome/browser/browser_main.cc
+++ b/chrome/browser/browser_main.cc
@@ -273,9 +273,10 @@ MetricsService* BrowserMainParts::SetupMetricsAndFieldTrials(
   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(