Allow generation of a chromium outdirs when enable_extensions=false

extensions/shell/common/api/BUILD.gn

 # Copyright 2014 The Chromium Authors. All rights reserved.
 # 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"
 
 json_schema_api("api") {
   sources = schema_sources
   schemas = true
   bundle = true
   bundle_name = "Shell"
 }
 
@@ skipping 43 matching lines @@
 }
 
 group("extensions_features") {
   public_deps = [
     ":shell_api_features",
     ":shell_behavior_features",
     ":shell_manifest_features",
     ":shell_permission_features",
   ]
 }