Add full SetThreadPriority support to Windows.

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..59345b005db13c26d2e80e5637d54d8c05ece90b 100644
--- a/base/threading/platform_thread_mac.mm
+++ b/base/threading/platform_thread_mac.mm
@@ -173,6 +173,12 @@ void PlatformThread::SetThreadPriority(PlatformThreadHandle handle,
   }
 }
 
+// static
+ThreadPriority PlatformThread::GetThreadPriority(PlatformThreadHandle handle) {
+  NOTIMPLEMENTED();
+  return kThreadPriority_Normal;
+}
+
 size_t GetDefaultThreadStackSize(const pthread_attr_t& attributes) {
 #if defined(OS_IOS)
   return 0;