Add MessageLoop::AssertIdle(). Use in ChromeOS audio threads.

chrome/browser/chromeos/audio_mixer_pulse.cc

Index: chrome/browser/chromeos/audio_mixer_pulse.cc
diff --git a/chrome/browser/chromeos/audio_mixer_pulse.cc b/chrome/browser/chromeos/audio_mixer_pulse.cc
index 42b268a3b77a5c6c5e509307cfcd596a5ccc4395..b5817bc9ba3ec13f7b9bd3a708cc2fd6e0e7e43e 100644
--- a/chrome/browser/chromeos/audio_mixer_pulse.cc
+++ b/chrome/browser/chromeos/audio_mixer_pulse.cc
@@ -7,6 +7,7 @@
 #include <pulse/pulseaudio.h>
 
 #include "base/logging.h"
+#include "base/message_loop.h"
 #include "base/task.h"
 #include "base/threading/thread_restrictions.h"
 
@@ -64,6 +65,7 @@ AudioMixerPulse::~AudioMixerPulse() {
     // The worker thread should be idle at this time.
     // See http://crosbug.com/11110 for discussion.
     base::ThreadRestrictions::ScopedAllowIO allow_io_for_thread_join;
+    thread_->message_loop()->AssertIdle();
 
     thread_->Stop();
     thread_.reset();
@@ -468,4 +470,3 @@ inline bool AudioMixerPulse::MainloopLockIfReady() const {
 }
 
 }  // namespace chromeos
-