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

gin/gin_features.cc

 // 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 "gin/public/gin_features.h"
 
 namespace features {
 
-// Enables or disables the future compiler pipeline of V8, with the Ignition
-// interpreter and TurboFan compiler.
+// Enables future experimental features of V8.
 const base::Feature kV8Future {
   "V8Future", base::FEATURE_DISABLED_BY_DEFAULT
 };
 
+// Disables the new compiler pipeline of V8, with the Ignition interpreter and
+// TurboFan compiler.
+const base::Feature kV8NoTurbo{"V8NoTurbo", base::FEATURE_DISABLED_BY_DEFAULT};
+
 // Enables or disables the V8 Ignition interpreter on low end
 // Android devices.
 const base::Feature kV8IgnitionLowEnd {
   "V8IgnitionLowEnd", base::FEATURE_ENABLED_BY_DEFAULT
 };
 
 }  // namespace features