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

base/message_loop.h

Index: base/message_loop.h
diff --git a/base/message_loop.h b/base/message_loop.h
index 7a3af6ef885800d34bf41c9ec274efcda4d8a8fd..8b51842472765e6f03e80ac4bb32f4c20c272127 100644
--- a/base/message_loop.h
+++ b/base/message_loop.h
@@ -315,6 +315,10 @@ class MessageLoop : public base::MessagePump::Delegate {
   // for at least 1s.
   static const int kHighResolutionTimerModeLeaseTimeMs = 1000;
 
+  // Asserts that the MessageLoop is "idle". in reality, we only check
+  // |incoming_queue_|, since we don't want to lock |work_queue_|.
+  void AssertIdle() const;
+
   //----------------------------------------------------------------------------
  protected:
   struct RunState {
@@ -461,12 +465,12 @@ class MessageLoop : public base::MessagePump::Delegate {
   scoped_refptr<base::Histogram> message_histogram_;
 
   // A null terminated list which creates an incoming_queue of tasks that are
-  // aquired under a mutex for processing on this instance's thread. These tasks
+  // acquired under a mutex for processing on this instance's thread. These tasks
   // have not yet been sorted out into items for our work_queue_ vs items that
   // will be handled by the TimerManager.
   TaskQueue incoming_queue_;
   // Protect access to incoming_queue_.
-  base::Lock incoming_queue_lock_;
+  mutable base::Lock incoming_queue_lock_;
 
   RunState* state_;