Allow generation of a chromium outdirs when enable_extensions=false

extensions/browser/api/BUILD.gn

 # Copyright 2016 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/common/api/schema.gni")
+import("//extensions/features/features.gni")
 import("//tools/json_schema_compiler/json_schema_api.gni")
 
+assert(enable_extensions,
+       "Cannot depend on extensions because enable_extensions=false.")
+
 source_set("api") {
   sources = [
     "api_resource.cc",
     "api_resource.h",
     "api_resource_manager.h",
     "async_api_function.cc",
     "async_api_function.h",
     "device_permissions_manager.cc",
     "device_permissions_manager.h",
     "device_permissions_prompt.cc",
@@ skipping 119 matching lines @@
   root_namespace = extensions_api_root_namespace
   uncompiled_sources = extensions_api_uncompiled_sources
 
   deps = [
     ":api",
     "//device/serial",
     "//extensions/common/api",
     "//skia",
   ]
 }