[TaskScheduler] Support TaskRunnerHandles from parallel tasks.

base/task_scheduler/scheduler_thread_pool_impl.cc

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "base/task_scheduler/scheduler_thread_pool_impl.h"
 
 #include <stddef.h>
 
 #include <algorithm>
 #include <utility>
@@ skipping 31 matching lines @@
   // long as |thread_pool| is alive.
   // TODO(robliao): Find a concrete way to manage |thread_pool|'s memory.
   SchedulerParallelTaskRunner(const TaskTraits& traits,
                               SchedulerThreadPool* thread_pool)
       : traits_(traits), thread_pool_(thread_pool) {}
 
   // TaskRunner:
   bool PostDelayedTask(const tracked_objects::Location& from_here,
                        const Closure& closure,
                        TimeDelta delay) override {
+    std::unique_ptr<Task> task(new Task(from_here, closure, traits_, delay));
+    task->task_runner_ref = this;
+
     // Post the task as part of a one-off single-task Sequence.
     return thread_pool_->PostTaskWithSequence(
-        WrapUnique(new Task(from_here, closure, traits_, delay)),
-        make_scoped_refptr(new Sequence), nullptr);
+        std::move(task), make_scoped_refptr(new Sequence), nullptr);
   }
 
   bool RunsTasksOnCurrentThread() const override {
     return tls_current_thread_pool.Get().Get() == thread_pool_;
   }
 
  private:
   ~SchedulerParallelTaskRunner() override = default;
 
   const TaskTraits traits_;
@@ skipping 495 matching lines @@
 }
 
 void SchedulerThreadPoolImpl::RemoveFromIdleWorkerThreadsStack(
     SchedulerWorkerThread* worker_thread) {
   AutoSchedulerLock auto_lock(idle_worker_threads_stack_lock_);
   idle_worker_threads_stack_.Remove(worker_thread);
 }
 
 }  // namespace internal
 }  // namespace base