GN: Replace mojo/system.gni with forwarding groups

mojo/common/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("//mojo/system.gni")
-
 # GYP version: mojo/mojo_base.gyp:mojo_common_lib
 component("common") {
   output_name = "mojo_common_lib"
 
   sources = [
     "common_type_converters.cc",
     "common_type_converters.h",
     "data_pipe_utils.cc",
     "data_pipe_utils.h",
     "handle_watcher.cc",
     "handle_watcher.h",
     "message_pump_mojo.cc",
     "message_pump_mojo.h",
     "message_pump_mojo_handler.h",
     "time_helper.cc",
     "time_helper.h",
   ]
 
   defines = [ "MOJO_COMMON_IMPLEMENTATION" ]
 
   deps = [
     "//base",
     "//base/third_party/dynamic_annotations",
+    "//mojo/public/c/system:for_component",
     "//url",
-  ] + mojo_system_for_component
+  ]
 }
 
 # GYP version: mojo/mojo_base.gyp:mojo_common_unittests
 test("mojo_common_unittests") {
   deps = [
     ":common",
     "//base",
     "//base:message_loop_tests",
     "//mojo/common/test:run_all_unittests",
     "//mojo/common/test:test_support",
     "//mojo/environment:chromium",
     "//mojo/public/cpp/bindings",
     "//mojo/public/cpp/test_support:test_utils",
     "//testing/gtest",
     "//url",
   ]
 
   sources = [
     "common_type_converters_unittest.cc",
     "handle_watcher_unittest.cc",
     "message_pump_mojo_unittest.cc",
     "test/multiprocess_test_helper_unittest.cc",
   ]
 }