Add service unittest for WakeLockServiceImpl.

device/wake_lock/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.
 
 source_set("wake_lock") {
   sources = [
     "wake_lock_provider.cc",
     "wake_lock_provider.h",
     "wake_lock_service_context.cc",
     "wake_lock_service_context.h",
     "wake_lock_service_impl.cc",
     "wake_lock_service_impl.h",
+    "wake_lock_service_impl_for_testing.cc",
+    "wake_lock_service_impl_for_testing.h",
   ]
 
   public_deps = [
     "//base",
     "//device/wake_lock/public/interfaces",
     "//mojo/public/cpp/bindings",
     "//ui/gfx",
   ]
 
   deps = [
     "//device/power_save_blocker",
   ]
 }