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

media/blink/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.
 
 import("//media/media_options.gni")
 import("//testing/test.gni")
 
 component("blink") {
   output_name = "media_blink"
 
@@ skipping 107 matching lines @@
     "run_all_unittests.cc",
     "test_response_generator.cc",
     "test_response_generator.h",
     "video_frame_compositor_unittest.cc",
     "webaudiosourceprovider_impl_unittest.cc",
   ]
 
   if (is_android) {
     deps += [ "//ui/gl" ]
   }
+
+  configs += [ "//v8:external_startup_data" ]
 }
 
 # TODO(GYP): Delete this after we've converted everything to GN.
 # The _run targets exist only for compatibility w/ GYP.
 group("media_blink_unittests_run") {
   testonly = true
   deps = [
     ":media_blink_unittests",
   ]
 }