Update from https://crrev.com/327068

base/threading/platform_thread_mac.mm

Index: base/threading/platform_thread_mac.mm
diff --git a/base/threading/platform_thread_mac.mm b/base/threading/platform_thread_mac.mm
index 147e625dbc8b2acc6d9707e35bc6fa28f943a715..fd40d7952c3bc9d1bf7c049629fce7a74b135373 100644
--- a/base/threading/platform_thread_mac.mm
+++ b/base/threading/platform_thread_mac.mm
@@ -161,10 +161,10 @@ void PlatformThread::SetThreadPriority(PlatformThreadHandle handle,
   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:
@@ -173,6 +173,12 @@ void PlatformThread::SetThreadPriority(PlatformThreadHandle handle,
   }
 }
 
+// static
+ThreadPriority PlatformThread::GetThreadPriority(PlatformThreadHandle handle) {
+  NOTIMPLEMENTED();
+  return ThreadPriority::NORMAL;
+}
+
 size_t GetDefaultThreadStackSize(const pthread_attr_t& attributes) {
 #if defined(OS_IOS)
   return 0;