Add support for real-time audio threads.

base/threading/simple_thread.h

Index: base/threading/simple_thread.h
===================================================================
--- base/threading/simple_thread.h	(revision 83935)
+++ base/threading/simple_thread.h	(working copy)
@@ -104,6 +104,12 @@
   // Overridden from PlatformThread::Delegate:
   virtual void ThreadMain();
 
+  // Enables time-contraint policy and priority suitable for low-latency,
+  // glitch-resistant audio.
+  void EnableRealtimeAudioPerformance() {
+    PlatformThread::EnableRealtimeAudioPerformance(thread_);
+  }
+
  private:
   const std::string name_prefix_;
   std::string name_;