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

content/app/BUILD.gn

Index: content/app/BUILD.gn
diff --git a/content/app/BUILD.gn b/content/app/BUILD.gn
index d8f67912097511b30d267305abfaf6274572ed26..d3a5e162a45659b55cfc93e552128573f31db535 100644
--- a/content/app/BUILD.gn
+++ b/content/app/BUILD.gn
@@ -3,6 +3,7 @@
 # found in the LICENSE file.
 
 import("//build/config/chrome_build.gni")
+import("//build_overrides/v8.gni")
 
 content_app_sources = [
   "android/app_jni_registrar.cc",
@@ -72,6 +73,10 @@ content_app_extra_configs = [
   "//content:content_implementation",
 ]
 
+if (v8_use_external_startup_data) {
+  content_app_extra_configs += [ "//v8:external_startup_data" ]
+}
+
 if (!is_multi_dll_chrome) {
   content_app_deps += [ "//content/gpu:gpu_sources" ]
 }