[TaskScheduler] Support TaskRunnerHandles from parallel tasks.

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 9e85b5cfc17b7b58c890e964294fbfc0f3680e72..364bb672cf9d51639378917f6775a1ccdac73bff 100644
--- a/base/task_scheduler/task_tracker.cc
+++ b/base/task_scheduler/task_tracker.cc
@@ -7,9 +7,8 @@
 #include "base/callback.h"
 #include "base/debug/task_annotator.h"
 #include "base/metrics/histogram_macros.h"
-#include "base/threading/sequenced_task_runner_handle.h"
+#include "base/threading/task_runner_handle.h"
 #include "base/threading/thread_restrictions.h"
-#include "base/threading/thread_task_runner_handle.h"
 #include "base/trace_event/trace_event.h"
 
 namespace base {
@@ -95,16 +94,23 @@ void TaskTracker::RunTask(const Task* task) {
 
   {
     // Set up TaskRunnerHandle as expected for the scope of the task.
-    std::unique_ptr<SequencedTaskRunnerHandle> sequenced_task_runner_handle;
-    std::unique_ptr<ThreadTaskRunnerHandle> single_thread_task_runner_handle;
-    DCHECK(!task->sequenced_task_runner_ref ||
-           !task->single_thread_task_runner_ref);
-    if (task->sequenced_task_runner_ref) {
-      sequenced_task_runner_handle.reset(
-          new SequencedTaskRunnerHandle(task->sequenced_task_runner_ref));
-    } else if (task->single_thread_task_runner_ref) {
-      single_thread_task_runner_handle.reset(
-          new ThreadTaskRunnerHandle(task->single_thread_task_runner_ref));
+    std::unique_ptr<TaskRunnerHandle::TaskScope> task_scope;
+    std::unique_ptr<TaskRunnerHandle::SequencedTaskScope> sequenced_task_scope;
+    std::unique_ptr<TaskRunnerHandle::SingleThreadTaskScope>
+        single_thread_task_scope;
+    if (task->task_runner_ref) {
+      DCHECK(!task->sequenced_task_runner_ref &&
+             !task->single_thread_task_runner_ref);
+      task_scope.reset(new TaskRunnerHandle::TaskScope(task->task_runner_ref));
+    } else if (task->sequenced_task_runner_ref) {
+      DCHECK(!task->single_thread_task_runner_ref);
+      sequenced_task_scope.reset(new TaskRunnerHandle::SequencedTaskScope(
+          task->sequenced_task_runner_ref));
+    } else {
+      DCHECK(task->single_thread_task_runner_ref);
+      single_thread_task_scope.reset(
+          new TaskRunnerHandle::SingleThreadTaskScope(
+              task->single_thread_task_runner_ref));
     }
 
     TRACE_TASK_EXECUTION(kRunFunctionName, *task);