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

media/blink/BUILD.gn

Index: media/blink/BUILD.gn
diff --git a/media/blink/BUILD.gn b/media/blink/BUILD.gn
index eb0661b55fa57475ab023274a0ffa8fbc944a5f6..92605306d86716d13eae3c589a9f29c60870cb8d 100644
--- a/media/blink/BUILD.gn
+++ b/media/blink/BUILD.gn
@@ -2,6 +2,7 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
+import("//build_overrides/v8.gni")
 import("//media/media_options.gni")
 import("//testing/test.gni")
 
@@ -125,6 +126,10 @@ test("media_blink_unittests") {
   if (is_android) {
     deps += [ "//ui/gl" ]
   }
+
+  if (v8_use_external_startup_data) {
+    configs += [ "//v8:external_startup_data" ]
+  }
 }
 
 # TODO(GYP): Delete this after we've converted everything to GN.