TaskScheduler [11] Support ExecutionMode::SINGLE_THREADED.

base/task_scheduler/scheduler_worker_thread.h

Index: base/task_scheduler/scheduler_worker_thread.h
diff --git a/base/task_scheduler/scheduler_worker_thread.h b/base/task_scheduler/scheduler_worker_thread.h
index 3022d100c61239b863c51d95b64e0252ef1360f1..5de245dcb019a3846b52e57368df2c29e84bd7da 100644
--- a/base/task_scheduler/scheduler_worker_thread.h
+++ b/base/task_scheduler/scheduler_worker_thread.h
@@ -37,8 +37,8 @@ class BASE_EXPORT SchedulerWorkerThread : public PlatformThread::Delegate {
    public:
     virtual ~Delegate() = default;
 
-    // Called when the main function of the SchedulerWorkerThread enters.
-    virtual void OnMainEntry() = 0;
+    // Called by |worker_thread| when it enters its main function.
+    virtual void OnMainEntry(SchedulerWorkerThread* worker_thread) = 0;
 
     // Called by |worker_thread| to get a Sequence from which to run a Task.
     virtual scoped_refptr<Sequence> GetWork(
@@ -68,6 +68,8 @@ class BASE_EXPORT SchedulerWorkerThread : public PlatformThread::Delegate {
   // returned by the GetWork() method of its delegate until it returns nullptr.
   void WakeUp();
 
+  SchedulerWorkerThread::Delegate* delegate() { return delegate_.get(); }
+
   // Joins this SchedulerWorkerThread. If a Task is already running, it will be
   // allowed to complete its execution. This can only be called once.
   void JoinForTesting();