EDK: Split the mojo_edk_system_unittests target.

mojo/edk/system/test/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")
 
 # Utilties for use by EDK internal (unit and perf) tests.
 mojo_edk_source_set("test") {
   testonly = true
   mojo_edk_visibility = [ "mojo/edk/*" ]
@@ skipping 73 matching lines @@
   sources = [
     "run_all_perftests.cc",
   ]
 
   deps = [
     ":test",
     "//base/test:test_support",
   ]
 }
 
-mojo_edk_source_set("unittests") {
-  testonly = true
-  mojo_edk_visibility = [ "mojo/edk/system:mojo_edk_system_unittests" ]
-
+mojo_edk_unittests("mojo_edk_system_test_unittests") {
   sources = [
     "random_unittest.cc",
   ]
 
   deps = [
     ":test",
     "//testing/gtest",
   ]
 }