Implement the WindowsLogoffRace finch experiment.

chrome/browser/chrome_browser_field_trials.cc

 // Copyright (c) 2012 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/chrome_browser_field_trials.h"
 
 #include <string>
 
 #include "base/command_line.h"
 #include "base/metrics/field_trial.h"
@@ skipping 39 matching lines @@
 }
 
 void ChromeBrowserFieldTrials::InstantiateDynamicTrials() {
   // Call |FindValue()| on the trials below, which may come from the server, to
   // ensure they get marked as "used" for the purposes of data reporting.
   base::FieldTrialList::FindValue("UMA-Dynamic-Binary-Uniformity-Trial");
   base::FieldTrialList::FindValue("UMA-Dynamic-Uniformity-Trial");
   base::FieldTrialList::FindValue("InstantDummy");
   base::FieldTrialList::FindValue("InstantChannel");
   base::FieldTrialList::FindValue("Test0PercentDefault");
+  base::FieldTrialList::FindValue("WindowsLogoffRace");

[Alexei Svitkine (slow), 2014/07/14 18:55:02]

I don't think this is necessary since your experiment runs entirely in the
browser process.

[Sigurður Ásgeirsson, 2014/07/14 20:31:38]

I don't know how this machinery works, but the comment above leads me to believe
that my experiment will never be "used" until logoff. The metric I'm after will
however be reported right after launch, e.g. the unclean shutdown count.

Are you sure I'm good without this?
I guess I'm asking whether all UMA reports contain the experiment groups that
client is enlisted in?

[Alexei Svitkine (slow), 2014/07/14 21:40:32]

Having the trial start in "active" state makes sense. Still, you don't need this
line as that can be done from the server-side with a starts_active:true flag.

   // The following trials are used from renderer process.
   // Mark here so they will be sync-ed.
   base::FieldTrialList::FindValue("CLD1VsCLD2");
   base::FieldTrialList::FindValue("MouseEventPreconnect");
   base::FieldTrialList::FindValue("UnauthorizedPluginInfoBar");
   // Activate the autocomplete dynamic field trials.
   OmniboxFieldTrial::ActivateDynamicTrials();
 }