base: Set initial thread priority in ThreadFunc.

base/threading/platform_thread.h

Index: base/threading/platform_thread.h
diff --git a/base/threading/platform_thread.h b/base/threading/platform_thread.h
index e2b09bcb5bfd01f8d69346f5b9e262b712b9b6fc..e62eb2b2c18475adeeb902f6b248e023dae69b2c 100644
--- a/base/threading/platform_thread.h
+++ b/base/threading/platform_thread.h
@@ -182,7 +182,8 @@ class BASE_EXPORT PlatformThread {
 
   // Toggles the current thread's priority at runtime. A thread may not be able
   // to raise its priority back up after lowering it if the process does not
-  // have a proper permission, e.g. CAP_SYS_NICE on Linux.
+  // have a proper permission, e.g. CAP_SYS_NICE on Linux. A thread may not be
+  // able to lower its priority back down after raising it to REALTIME_AUDIO.
   // Since changing other threads' priority is not permitted in favor of
   // security, this interface is restricted to change only the current thread
   // priority (https://crbug.com/399473).