Turn ThreadPriority enum into an enum class.

base/threading/platform_thread_mac.mm

 // Copyright (c) 2012 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.
 
 #include "base/threading/platform_thread.h"
 
 #import <Foundation/Foundation.h>
 #include <mach/mach.h>
 #include <mach/mach_time.h>
 #include <mach/thread_policy.h>
@@ skipping 143 matching lines @@
 
 }  // anonymous namespace
 
 // static
 void PlatformThread::SetThreadPriority(PlatformThreadHandle handle,
                                        ThreadPriority priority) {
   // Convert from pthread_t to mach thread identifier.
   mach_port_t mach_thread_id = pthread_mach_thread_np(handle.handle_);
 
   switch (priority) {
-    case kThreadPriority_Normal:
+    case ThreadPriority::NORMAL:
       SetPriorityNormal(mach_thread_id);
       break;
-    case kThreadPriority_RealtimeAudio:
+    case ThreadPriority::REALTIME_AUDIO:
       SetPriorityRealtimeAudio(mach_thread_id);
       break;
     default:
       NOTREACHED() << "Unknown priority.";
       break;
   }
 }
 
 // static
 ThreadPriority PlatformThread::GetThreadPriority(PlatformThreadHandle handle) {
   NOTIMPLEMENTED();
-  return kThreadPriority_Normal;
+  return ThreadPriority::NORMAL;
 }
 
 size_t GetDefaultThreadStackSize(const pthread_attr_t& attributes) {
 #if defined(OS_IOS)
   return 0;
 #else
   // The Mac OS X default for a pthread stack size is 512kB.
   // Libc-594.1.4/pthreads/pthread.c's pthread_attr_init uses
   // DEFAULT_STACK_SIZE for this purpose.
   //
@@ skipping 24 matching lines @@
 #endif
 }
 
 void InitOnThread() {
 }
 
 void TerminateOnThread() {
 }
 
 }  // namespace base