Control ES2015 'Tail call elimination' language feature via finch flag.

chrome/renderer/chrome_render_process_observer.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/renderer/chrome_render_process_observer.h"
 
 #include <stddef.h>
 #include <limits>
 #include <set>
 #include <utility>
 #include <vector>
 
 #include "base/base_switches.h"
 #include "base/bind.h"
 #include "base/command_line.h"
+#include "base/feature_list.h"
 #include "base/files/file_util.h"
 #include "base/location.h"
 #include "base/macros.h"
 #include "base/memory/weak_ptr.h"
 #include "base/metrics/field_trial.h"
 #include "base/metrics/histogram.h"
 #include "base/metrics/statistics_recorder.h"
 #include "base/path_service.h"
 #include "base/single_thread_task_runner.h"
 #include "base/strings/utf_string_conversions.h"
@@ skipping 200 matching lines @@
 
   DISALLOW_COPY_AND_ASSIGN(ResourceUsageReporterImpl);
 };
 
 void CreateResourceUsageReporter(
     base::WeakPtr<ChromeRenderProcessObserver> observer,
     mojo::InterfaceRequest<ResourceUsageReporter> request) {
   new ResourceUsageReporterImpl(observer, std::move(request));
 }
 
+const base::Feature kV8_ES2015_TailCalls_Feature {
+  "V8_ES2015_TailCalls", base::FEATURE_DISABLED_BY_DEFAULT
+};
+
 }  // namespace
 
 bool ChromeRenderProcessObserver::is_incognito_process_ = false;
 
 ChromeRenderProcessObserver::ChromeRenderProcessObserver()
     : weak_factory_(this) {
   const base::CommandLine& command_line =
       *base::CommandLine::ForCurrentProcess();
 
 #if defined(ENABLE_AUTOFILL_DIALOG)
   WebRuntimeFeatures::enableRequestAutocomplete(true);
 #endif
 
+  if (base::FeatureList::IsEnabled(kV8_ES2015_TailCalls_Feature)) {
+    std::string flag("--harmony-tailcalls");
+    v8::V8::SetFlagsFromString(flag.c_str(), static_cast<int>(flag.size()));
+  }
+
   if (command_line.HasSwitch(switches::kDisableJavaScriptHarmonyShipping)) {
     std::string flag("--noharmony-shipping");
     v8::V8::SetFlagsFromString(flag.c_str(), static_cast<int>(flag.size()));
   }
 
   if (command_line.HasSwitch(switches::kJavaScriptHarmony)) {
     std::string flag("--harmony");
     v8::V8::SetFlagsFromString(flag.c_str(), static_cast<int>(flag.size()));
   }
 
@@ skipping 124 matching lines @@
 ChromeRenderProcessObserver::content_setting_rules() const {
   return &content_setting_rules_;
 }
 
 void ChromeRenderProcessObserver::OnFieldTrialGroupFinalized(
     const std::string& trial_name,
     const std::string& group_name) {
   content::RenderThread::Get()->Send(
       new ChromeViewHostMsg_FieldTrialActivated(trial_name));
 }