Allow generation of a chromium outdirs when enable_extensions=false

extensions/shell/common/api/BUILD.gn

Index: extensions/shell/common/api/BUILD.gn
diff --git a/extensions/shell/common/api/BUILD.gn b/extensions/shell/common/api/BUILD.gn
index a2aee1e96ad821b06b2ef58eb7ece60b9a2844b8..b91d68f6e18c3b4d820f5cb51ef4a3fb12bb6c4b 100644
--- a/extensions/shell/common/api/BUILD.gn
+++ b/extensions/shell/common/api/BUILD.gn
@@ -2,9 +2,13 @@
 # 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")
 import("//tools/json_schema_compiler/json_features.gni")
 import("//tools/json_schema_compiler/json_schema_api.gni")
 
+assert(enable_extensions,
+       "Cannot depend on extensions because enable_extensions=false.")
+
 schema_sources = [ "identity.idl" ]
 root_namespace = "extensions::shell::api::%(namespace)s"