[Gin] Add V8NoTurbo experiment to disable Ignition+TurboFan.

gin/v8_initializer.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 "gin/v8_initializer.h"
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include <memory>
@@ skipping 349 matching lines @@
   if (IsolateHolder::kStrictMode == mode) {
     static const char use_strict[] = "--use_strict";
     v8::V8::SetFlagsFromString(use_strict, sizeof(use_strict) - 1);
   }
   if (IsolateHolder::kStableAndExperimentalV8Extras == v8_extras_mode) {
     static const char flag[] = "--experimental_extras";
     v8::V8::SetFlagsFromString(flag, sizeof(flag) - 1);
   }
 
   const char* ignition_enabled_crash_key = "N";
-  if (base::FeatureList::IsEnabled(features::kV8Future)) {
+  if (base::FeatureList::IsEnabled(features::kV8NoTurbo)) {
+    ignition_enabled_crash_key = "N";
+    std::string flag("--no-turbo");
+    v8::V8::SetFlagsFromString(flag.c_str(), static_cast<int>(flag.size()));
+  } else if (base::FeatureList::IsEnabled(features::kV8Future)) {
     ignition_enabled_crash_key = "Y";
     std::string flag("--future");
     v8::V8::SetFlagsFromString(flag.c_str(), static_cast<int>(flag.size()));
   } else if (base::FeatureList::IsEnabled(features::kV8IgnitionLowEnd) &&
              base::SysInfo::IsLowEndDevice()) {
     ignition_enabled_crash_key = "Y";
     std::string flag("--ignition");
     v8::V8::SetFlagsFromString(flag.c_str(), static_cast<int>(flag.size()));
   }
   static const char kIgnitionEnabledKey[] = "v8-ignition";
@@ skipping 37 matching lines @@
     *snapshot_data_out =
         reinterpret_cast<const char*>(g_mapped_snapshot->data());
     *snapshot_size_out = static_cast<int>(g_mapped_snapshot->length());
   } else {
     *snapshot_data_out = NULL;
     *snapshot_size_out = 0;
   }
 }
 
 }  // namespace gin