Add trace code to track all posted tasks in message_loop.

base/threading/worker_pool_win.cc

Index: base/threading/worker_pool_win.cc
diff --git a/base/threading/worker_pool_win.cc b/base/threading/worker_pool_win.cc
index 2aa423f035bd46334546a0a138563f5ae6b6b637..a840b57e95039f9f861860f8df0f684d07305b44 100644
--- a/base/threading/worker_pool_win.cc
+++ b/base/threading/worker_pool_win.cc
@@ -5,6 +5,7 @@
 #include "base/threading/worker_pool.h"
 
 #include "base/bind.h"
+#include "base/debug/trace_event.h"
 #include "base/logging.h"
 #include "base/task.h"
 #include "base/tracked_objects.h"
@@ -17,7 +18,8 @@ struct PendingTask {
   PendingTask(
       const tracked_objects::Location& posted_from,
       const base::Closure& task)
-      : task(task) {
+      : posted_from(posted_from),
+        task(task) {
 #if defined(TRACK_ALL_TASK_OBJECTS)
     post_births = tracked_objects::ThreadData::TallyABirthIfActive(posted_from);
     time_posted = TimeTicks::Now();
@@ -32,12 +34,18 @@ struct PendingTask {
   TimeTicks time_posted;
 #endif  // defined(TRACK_ALL_TASK_OBJECTS)
 
+  // The site this PendingTask was posted from.
+  tracked_objects::Location posted_from;
+
   // The task to run.
   base::Closure task;
 };
 
 DWORD CALLBACK WorkItemCallback(void* param) {
   PendingTask* pending_task = static_cast<PendingTask*>(param);
+  TRACE_EVENT2("base", "WorkItemCallback",
+      "src_file", pending_task->posted_from.file_line(),
+      "src_func", pending_task->posted_from.function_name().data());
   pending_task->task.Run();
 #if defined(TRACK_ALL_TASK_OBJECTS)
   tracked_objects::ThreadData::TallyADeathIfActive(