Use queue label as id in SequencedTaskChecker when not running on TaskQueue

webrtc/base/sequenced_task_checker_impl.cc

Index: webrtc/base/sequenced_task_checker_impl.cc
diff --git a/webrtc/base/sequenced_task_checker_impl.cc b/webrtc/base/sequenced_task_checker_impl.cc
index 615f44c2b52e8562c182159748b418c4b40729ce..3e28ea171b7ba7dc6418584bdc149b99abf4dec9 100644
--- a/webrtc/base/sequenced_task_checker_impl.cc
+++ b/webrtc/base/sequenced_task_checker_impl.cc
@@ -22,7 +22,13 @@ SequencedTaskCheckerImpl::SequencedTaskCheckerImpl()
 SequencedTaskCheckerImpl::~SequencedTaskCheckerImpl() {}
 
 bool SequencedTaskCheckerImpl::CalledSequentially() const {
-  TaskQueue* current_queue = TaskQueue::Current();
+  QueueId current_queue = TaskQueue::Current();
+#if defined(WEBRTC_MAC)
+  if (current_queue == nullptr)
+    // If we're not running on a TaskQueue, use the system dispatch queue

[magjed_webrtc, 2016/11/02 12:04:41]

nit: I would like the comments above the if-statement instead.

[tommi, 2016/11/02 16:32:50]

agree.
style comment: as is, this should use {} since the body of the conditional,
including comments, is more than one line.

[kthelgason, 2016/11/02 16:53:55]

Done.

+    // label as an identifier.
+    current_queue = dispatch_queue_get_label(DISPATCH_CURRENT_QUEUE_LABEL);

[magjed_webrtc, 2016/11/02 12:04:41]

We don't need any include for this magical dispatch_queue_get_label?

[tommi, 2016/11/02 16:32:50]

good point.  We need #include <dispatch/dispatch.h> which is transitively
included right now via task_queue.h.

[kthelgason, 2016/11/02 16:53:55]

Done.

+#endif
   CritScope scoped_lock(&lock_);
   if (!attached_) {  // true if previously detached.
     valid_queue_ = current_queue;