base: Set initial thread priority in ThreadFunc.

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 164 matching lines @@
   // PlatformThreadHandle.
   static bool CreateNonJoinable(size_t stack_size, Delegate* delegate);
 
   // Joins with a thread created via the Create function.  This function blocks
   // the caller until the designated thread exits.  This will invalidate
   // |thread_handle|.
   static void Join(PlatformThreadHandle thread_handle);
 
   // 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).
   static void SetCurrentThreadPriority(ThreadPriority priority);
 
   static ThreadPriority GetCurrentThreadPriority();
 
  private:
   DISALLOW_IMPLICIT_CONSTRUCTORS(PlatformThread);
 };
 
 }  // namespace base
 
 #endif  // BASE_THREADING_PLATFORM_THREAD_H_