Adding more detail to MessageQueue::Dispatch logging.

Every message will now be traced with the location from which it was
posted, including function name, file and line number.

This CL also writes a normal LOG message when the dispatch took more
than a certain amount of time (currently 50ms).

This logging should help us identify messages that are taking
longer than expected to be dispatched.

R=pthatcher@webrtc.org, tommi@webrtc.org

Review URL: https://codereview.webrtc.org/2019423006 .

Cr-Commit-Position: refs/heads/master@{#13104}
diff --git a/webrtc/base/worker.cc b/webrtc/base/worker.cc
index 1b48b9b..f31c43f 100644
--- a/webrtc/base/worker.cc
+++ b/webrtc/base/worker.cc
@@ -63,7 +63,7 @@
 
 void Worker::HaveWork() {
   ASSERT(worker_thread_ != NULL);
-  worker_thread_->Post(this, MSG_HAVEWORK);
+  worker_thread_->Post(RTC_FROM_HERE, this, MSG_HAVEWORK);
 }
 
 void Worker::OnMessage(rtc::Message *msg) {