Move v8_use_external_startup_data out of //build/config:feature_flags.

chrome/plugin/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.
 
 static_library("plugin") {
   sources = [
     "chrome_content_plugin_client.cc",
     "chrome_content_plugin_client.h",
   ]
 
-  configs += [ "//build/config/compiler:wexit_time_destructors" ]
+  configs += [
+    "//build/config/compiler:wexit_time_destructors",
+    "//v8:external_startup_data",
+  ]
 
   deps = [
     "//base",
     "//chrome:strings",
     "//content/public/plugin",
     "//gin",
   ]
 }