Turn ThreadPriority enum into an enum class.

base/threading/platform_thread.h

 // 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.
 
 // WARNING: You should *NOT* be using this class directly.  PlatformThread is
 // the low-level platform-specific abstraction to the OS's threading interface.
 // You should instead be using a message-loop driven Thread, see thread.h.
 
 #ifndef BASE_THREADING_PLATFORM_THREAD_H_
 #define BASE_THREADING_PLATFORM_THREAD_H_
@@ skipping 92 matching lines @@
 
  private:
   friend class PlatformThread;
 
   Handle handle_;
   PlatformThreadId id_;
 };
 
 const PlatformThreadId kInvalidThreadId(0);
 
-// Valid values for SetThreadPriority()
-enum ThreadPriority {
-  kThreadPriority_Normal,
+// Valid values for SetThreadPriority(), listed in increasing order of
+// importance.
+enum class ThreadPriority {
+  // Suitable for threads that shouldn't disrupt high priority work.
+  BACKGROUND,
+  // Default priority level.
+  NORMAL,
+  // Suitable for threads which generate data for the display (at ~60Hz).
+  DISPLAY,
   // Suitable for low-latency, glitch-resistant audio.
-  kThreadPriority_RealtimeAudio,
-  // Suitable for threads which generate data for the display (at ~60Hz).
-  kThreadPriority_Display,
-  // Suitable for threads that shouldn't disrupt high priority work.
-  kThreadPriority_Background
+  REALTIME_AUDIO,
 };
 
 // A namespace for low-level thread functions.
 class BASE_EXPORT PlatformThread {
  public:
   // Implement this interface to run code on a background thread.  Your
   // ThreadMain method will be called on the newly created thread.
   class BASE_EXPORT Delegate {
    public:
     virtual void ThreadMain() = 0;
@@ skipping 62 matching lines @@
 
   static ThreadPriority GetThreadPriority(PlatformThreadHandle handle);
 
  private:
   DISALLOW_IMPLICIT_CONSTRUCTORS(PlatformThread);
 };
 
 }  // namespace base
 
 #endif  // BASE_THREADING_PLATFORM_THREAD_H_