Allow overriding variation parameter via chrome://flags.

chrome/browser/chrome_browser_main.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_main.h"
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include <set>
@@ skipping 700 matching lines @@
     // X-Client-Data request header.
     variations::VariationsHttpHeaderProvider* provider =
         variations::VariationsHttpHeaderProvider::GetInstance();
     bool result = provider->SetDefaultVariationIds(
         command_line->GetSwitchValueASCII(switches::kForceVariationIds));
     CHECK(result) << "Invalid --" << switches::kForceVariationIds
                   << " list specified.";
     metrics->AddSyntheticTrialObserver(provider);
   }
 
+  // Associate parameters chosen in about:flags and create trial/group for them.
+  // TODO(jkrcal): don't create flags_strorage_ twice in chrome_browser_main.cc.
+  flags_ui::PrefServiceFlagsStorage flags_storage_(

[Alexei Svitkine (slow), 2016/06/08 18:54:35]

Nit: Local vars shouldn't have their names end with _.

[jkrcal, 2016/06/09 09:55:15]

Done.

+      g_browser_process->local_state());
+  about_flags::RegisterFeatureVariationParameters(&flags_storage_);
+
   std::unique_ptr<base::FeatureList> feature_list(new base::FeatureList);
   feature_list->InitializeFromCommandLine(
       command_line->GetSwitchValueASCII(switches::kEnableFeatures),
       command_line->GetSwitchValueASCII(switches::kDisableFeatures));
 
 #if defined(FIELDTRIAL_TESTING_ENABLED)
   if (!command_line->HasSwitch(switches::kDisableFieldTrialTestingConfig) &&
       !command_line->HasSwitch(switches::kForceFieldTrials) &&
       !command_line->HasSwitch(variations::switches::kVariationsServerURL)) {
     chrome_variations::AssociateDefaultFieldTrialConfig(feature_list.get());
@@ skipping 1262 matching lines @@
   chromeos::CrosSettings::Shutdown();
 #endif  // defined(OS_CHROMEOS)
 #endif  // defined(OS_ANDROID)
 }
 
 // Public members:
 
 void ChromeBrowserMainParts::AddParts(ChromeBrowserMainExtraParts* parts) {
   chrome_extra_parts_.push_back(parts);
 }