Allow generation of a chromium outdirs when enable_extensions=false

extensions/components/javascript_dialog_extensions_client/BUILD.gn

Index: extensions/components/javascript_dialog_extensions_client/BUILD.gn
diff --git a/extensions/components/javascript_dialog_extensions_client/BUILD.gn b/extensions/components/javascript_dialog_extensions_client/BUILD.gn
index 7e05ed7eee53192786c540ce7ee8940be4f06acc..c55ddfef4770fe9469c10b6de36c1e25455e9462 100644
--- a/extensions/components/javascript_dialog_extensions_client/BUILD.gn
+++ b/extensions/components/javascript_dialog_extensions_client/BUILD.gn
@@ -2,6 +2,11 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
+import("//extensions/features/features.gni")
+
+assert(enable_extensions,
+       "Cannot depend on extensions because enable_extensions=false.")
+
 static_library("javascript_dialog_extensions_client") {
   sources = [
     "javascript_dialog_extension_client_impl.cc",