EDK: Split the mojo_edk_system_unittests target.

mojo/edk/util/BUILD.gn

 # Copyright 2015 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_edk.gni")
 
 mojo_edk_source_set("util") {
   sources = [
     "command_line.cc",
     "command_line.h",
@@ skipping 12 matching lines @@
     "thread_annotations.h",
     "waitable_event.cc",
     "waitable_event.h",
   ]
 
   mojo_edk_configs = [ "mojo/edk/system:system_config" ]
 
   mojo_sdk_public_deps = [ "mojo/public/cpp/system" ]
 }
 
-mojo_edk_source_set("unittests") {
-  testonly = true
-  mojo_edk_visibility = [ "mojo/edk/system:mojo_edk_system_unittests" ]
-
+mojo_edk_unittests("mojo_edk_util_unittests") {
   sources = [
     "command_line_unittest.cc",
     "cond_var_unittest.cc",
     "mutex_unittest.cc",
     "ref_counted_unittest.cc",
     "thread_annotations_unittest.cc",
     "waitable_event_unittest.cc",
   ]
 
   deps = [
@@ skipping 17 matching lines @@
   deps = [
     ":util",
     "//testing/gtest",
   ]
 
   mojo_edk_deps = [
     "mojo/edk/system/test",
     "mojo/edk/system/test:perf",
   ]
 }