Do not explicitly allow singletons in AudioDeviceThread.

media/audio/audio_device_thread.cc

Index: media/audio/audio_device_thread.cc
diff --git a/media/audio/audio_device_thread.cc b/media/audio/audio_device_thread.cc
index edbdbd89cedd42f32d83fed4999114c06b609255..0a0d274a00d48d72f38eefbd9e8032e3ca3873d8 100644
--- a/media/audio/audio_device_thread.cc
+++ b/media/audio/audio_device_thread.cc
@@ -7,7 +7,6 @@
 #include <limits>
 
 #include "base/logging.h"
-#include "base/threading/thread_restrictions.h"
 
 namespace media {
 
@@ -62,7 +61,6 @@ AudioDeviceThread::~AudioDeviceThread() {
 
 void AudioDeviceThread::ThreadMain() {
   base::PlatformThread::SetName(thread_name_);
-  base::ThreadRestrictions::SetSingletonAllowed(true);
   callback_->InitializeOnAudioThread();
 
   uint32_t buffer_index = 0;