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

content/public/common/BUILD.gn

Index: content/public/common/BUILD.gn
diff --git a/content/public/common/BUILD.gn b/content/public/common/BUILD.gn
index c207e84d9920edb5592db3cff6a25e2eaf916962..4182c8c405eda5b9ee1dc0ddec8c3fdf3ca8ac4b 100644
--- a/content/public/common/BUILD.gn
+++ b/content/public/common/BUILD.gn
@@ -3,6 +3,7 @@
 # found in the LICENSE file.
 
 import("//build/config/features.gni")
+import("//build_overrides/v8.gni")
 import("//content/common/common.gni")
 import("//third_party/mojo/src/mojo/public/tools/bindings/mojom.gni")
 
@@ -62,6 +63,10 @@ source_set("common_sources") {
     "//content:content_implementation",
   ]
 
+  if (v8_use_external_startup_data) {
+    public_configs = [ "//v8:external_startup_data" ]
+  }
+
   public_deps = [
     "//content/common",
     "//third_party/mojo/src/mojo/public/cpp/bindings",