TaskScheduler: Add TRACE_TASK_EXECUTION to TaskTracker::RunTask.

base/task_scheduler/task_tracker.cc

Index: base/task_scheduler/task_tracker.cc
diff --git a/base/task_scheduler/task_tracker.cc b/base/task_scheduler/task_tracker.cc
index f38ec06130e6bebfd77d469478a34dea93b34951..85ca67f43b2aff007c158ac3eae21e703bfd097f 100644
--- a/base/task_scheduler/task_tracker.cc
+++ b/base/task_scheduler/task_tracker.cc
@@ -10,6 +10,7 @@
 #include "base/thread_task_runner_handle.h"
 #include "base/threading/sequenced_task_runner_handle.h"
 #include "base/threading/thread_restrictions.h"
+#include "base/trace_event/trace_event.h"
 
 namespace base {
 namespace internal {
@@ -18,6 +19,10 @@ namespace {
 
 const char kQueueFunctionName[] = "base::PostTask";
 
+// This name conveys that a Task is run by the task scheduler without revealing
+// its implementation details.
+const char kRunFunctionName[] = "TaskSchedulerRunTask";
+
 // Upper bound for the
 // TaskScheduler.BlockShutdownTasksPostedDuringShutdown histogram.
 const HistogramBase::Sample kMaxBlockShutdownTasksPostedDuringShutdown = 1000;
@@ -102,6 +107,8 @@ void TaskTracker::RunTask(const Task* task) {
           new ThreadTaskRunnerHandle(task->single_thread_task_runner_ref));
     }
 
+    TRACE_TASK_EXECUTION(kRunFunctionName, *task);
+
     debug::TaskAnnotator task_annotator;
     task_annotator.RunTask(kQueueFunctionName, *task);
   }