Adjust interfaces to indicate when tracking is in progress

base/threading/worker_pool_posix.cc

Index: base/threading/worker_pool_posix.cc
===================================================================
--- base/threading/worker_pool_posix.cc	(revision 109037)
+++ base/threading/worker_pool_posix.cc	(working copy)
@@ -90,13 +90,13 @@
         "src_func", pending_task.posted_from.function_name());
 
     tracked_objects::TrackedTime start_time =
-        tracked_objects::ThreadData::Now();
+        tracked_objects::ThreadData::NowForStartOfRun();
 
     pending_task.task.Run();
 
     tracked_objects::ThreadData::TallyRunOnWorkerThreadIfTracking(
         pending_task.birth_tally, pending_task.time_posted,
-        start_time, tracked_objects::ThreadData::Now());
+        start_time, tracked_objects::ThreadData::NowForEndOfRun());
   }
 
   // The WorkerThread is non-joinable, so it deletes itself.