Getting answer server URL from the variations server.

ui/app_list/app_list_switches.cc

 // Copyright 2013 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 "ui/app_list/app_list_switches.h"
 
 #include "base/command_line.h"
+#include "base/metrics/field_trial_params.h"
 #include "build/build_config.h"
 
 namespace app_list {
 namespace switches {
 
 // If empty, search answers in the app app list are disabled, otherwise the URL
 // of the answer server.
 const char kAnswerServerUrl[] = "answer-server-url";
 
 // Specifies the chrome-extension:// URL for the contents of an additional page
@@ skipping 54 matching lines @@
     return true;
 
   if (base::CommandLine::ForCurrentProcess()->HasSwitch(
           kDisableDriveSearchInChromeLauncher))
     return false;
 
   return true;
 }
 
 std::string AnswerServerUrl() {
-  return base::CommandLine::ForCurrentProcess()->GetSwitchValueNative(
-      kAnswerServerUrl);
+  // If the answer server URL is passed in the command line, use it, otherwise
+  // get it from the variations server.
+  std::string variations_url = base::GetFieldTrialParamValue(

[xiyuan, 2017/04/26 23:18:00]

nit: get rid of |variations_url| and inline GetFieldTrialParamValue. So that we
only call it when there is no command line switch.

[vadimt, 2017/04/26 23:29:42]

See the links I'll send. Quote:

  // Note: It's important to query the field trial state first, to ensure that
  // UMA reports the correct group.

+      "SearchAnswerCard", switches::kAnswerServerUrl);
+  std::string url =

[xiyuan, 2017/04/26 23:18:00]

nit: const

[vadimt, 2017/04/26 23:29:42]

Done.
I like consts, but I'm not using them in Chrome since this doesn't seem to be a
common practice. I don't want my style to deviate from the average.

+      base::CommandLine::ForCurrentProcess()->GetSwitchValueNative(
+          kAnswerServerUrl);
+  return !url.empty() ? url : variations_url;
 }
 
 bool IsAnswerCardEnabled() {
-  return !AnswerServerUrl().empty();
+  static const bool enabled = !AnswerServerUrl().empty();
+  return enabled;
 }
 
 }  // namespace switches
 }  // namespace app_list