[tracing] Add task execution event for sequenced worker pool

base/threading/sequenced_worker_pool.cc

Index: base/threading/sequenced_worker_pool.cc
diff --git a/base/threading/sequenced_worker_pool.cc b/base/threading/sequenced_worker_pool.cc
index 24a07511a9847a4faba4dc855470cbda3fbb347b..758fbe72b766c6c7e7d6525f8995cf255700f247 100644
--- a/base/threading/sequenced_worker_pool.cc
+++ b/base/threading/sequenced_worker_pool.cc
@@ -810,6 +810,8 @@ void SequencedWorkerPool::Inner::ThreadLoop(Worker* this_worker) {
             TRACE_EVENT_FLAG_FLOW_IN,
             "src_file", task.posted_from.file_name(),
             "src_func", task.posted_from.function_name());
+        TRACE_EVENT_API_SCOPED_TASK_EXECUTION_EVENT INTERNAL_TRACE_EVENT_UID(

[Primiano Tucci (use gerrit), 2016/05/04 08:21:50]

you don't need EVENT INTERNAL_TRACE_EVENT_UID here.
1) as the name suggests it's internal :)
2) That is only used to disambiguate the local variable name when using the
TRACE_TASK_EXECUTION macro. Since here you are instantiating explicitly you can
just pick a name, e.g.
:

TRACE_EVENT_API_SCOPED_TASK_EXECUTION_EVENT
task_event(task.posted_from.file_name());

[ssid, 2016/05/06 03:15:26]

I added this because every time i didn't in past you had told me to add. yes it
is not required for this case. Sorry.

[Primiano Tucci (use gerrit), 2016/05/06 10:22:03]

Oops. I hope I didn't suggest in non-tracing code, that should be internal and
used only in macros.

+            task_event)(task.posted_from.file_name());
         int new_thread_id = WillRunWorkerTask(task);
         {
           AutoUnlock unlock(lock_);