Use CONTINUE_ON_SHUTDOWN for IncidentReportingService tasks.

chrome/browser/browser_hangs_experiment.cc

Index: chrome/browser/browser_hangs_experiment.cc
diff --git a/chrome/browser/browser_hangs_experiment.cc b/chrome/browser/browser_hangs_experiment.cc
new file mode 100644
index 0000000000000000000000000000000000000000..858a8e45b185249df6f2ce51e58ab4eeca660875
--- /dev/null
+++ b/chrome/browser/browser_hangs_experiment.cc
@@ -0,0 +1,28 @@
+// Copyright 2016 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_hangs_experiment.h"
+
+#include <string>
+
+#include "base/command_line.h"
+#include "base/metrics/field_trial.h"

[grt (UTC plus 2), 2016/04/25 13:37:53]

use base/feature_list.h instead of field_trial.h? the docs say that the former
supersedes the latter. it's a lot less typing (or copying-and-pasting, as the
case may be):

  return base::FeatureList::IsEnabled(kYourFeature);

[Patrick Monette, 2016/04/25 18:14:27]

Ooohh shiny!

+#include "base/strings/string_util.h"
+
+bool IsBrowserHangsExperimentEnabled() {
+  using base::CommandLine;
+
+  // Note: It's important to query the field trial state first, to ensure that
+  // UMA reports the correct group.

[manzagop (departed), 2016/04/25 13:37:39]

For my benefit, what gets reported in the case of an argument override? The
non-overridden value, right?

[Patrick Monette, 2016/04/25 18:14:27]

The whole experiment is set server-side. There is a concept of "forcing_flag"
while creating the experiment that will tell finch to consider people with those
flags on their command line as a separate group.

+  const std::string group_name =
+      base::FieldTrialList::FindFullName("BrowserHangsExperiment");
+  if (CommandLine::ForCurrentProcess()->HasSwitch(

[manzagop (departed), 2016/04/25 13:37:39]

Need to check InitializedForCurrentProcess first?

[Patrick Monette, 2016/04/25 18:14:27]

No longer using CommandLine::ForCurrentProcess().

+          "disable-browser-hangs-experiment"))
+    return false;
+  if (CommandLine::ForCurrentProcess()->HasSwitch(
+          "enable-browser-hangs-experiment"))
+    return true;
+
+  return base::StartsWith(group_name, "Enabled", base::CompareCase::SENSITIVE);

[manzagop (departed), 2016/04/25 13:37:39]

Where does "Enabled" come from? Is it a standard group prefix? Might it be
reused, eg in a test? Worth having a variable for it (constexpr)?

[Patrick Monette, 2016/04/25 18:14:27]

The only place it'll be reuse is in the finch config server-side.

+}