Enable ES6 generators

BUILD.gn

 # Copyright 2014 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.
 
 # TODO(jochen): These will need to be user-settable to support standalone V8
 # builds.
 v8_compress_startup_data = "off"
 v8_deprecation_warnings = false
 v8_enable_disassembler = false
 v8_enable_gdbjit = false
@@ skipping 171 matching lines @@
     "src/array.js",
     "src/string.js",
     "src/uri.js",
     "third_party/fdlibm/fdlibm.js",
     "src/math.js",
     "src/apinatives.js",
     "src/date.js",
     "src/regexp.js",
     "src/arraybuffer.js",
     "src/typedarray.js",
+    "src/generator.js",
     "src/object-observe.js",
     "src/collection.js",
     "src/weak-collection.js",
     "src/collection-iterator.js",
     "src/promise.js",
     "src/messages.js",
     "src/json.js",
     "src/array-iterator.js",
     "src/string-iterator.js",
     "src/debug-debugger.js",
@@ skipping 1180 matching lines @@
     deps = [
       ":v8_base",
       ":v8_nosnapshot",
     ]
   }
 
   direct_dependent_configs = [ ":external_config" ]
 }
 
 }