[Concurrency] Minor cleanups to futures.

Author: DougGregor

include/swift/ABI/Task.h

@@ -364,16 +364,17 @@ class AsyncTask : public HeapObject, public Job {
   /// executor.
   void completeFuture(AsyncContext *context, ExecutorRef executor);
 
+  static bool classof(const Job *job) {
+    return job->isAsyncTask();
+  }
+
+private:
   /// Access the next waiting task, which establishes a singly linked list of
   /// tasks that are waiting on a future.
   AsyncTask *&getNextWaitingTask() {
     return reinterpret_cast<AsyncTask *&>(
         SchedulerPrivate[NextWaitingTaskIndex]);
   }
-
-  static bool classof(const Job *job) {
-    return job->isAsyncTask();
-  }
 };
 
 // The compiler will eventually assume these.

stdlib/public/Concurrency/Task.cpp

@@ -97,7 +97,7 @@ void AsyncTask::completeFuture(AsyncContext *context, ExecutorRef executor) {
       newQueueHead, std::memory_order_acquire);
   assert(queueHead.getStatus() == Status::Executing);
 
-  // Notify every
+  // Schedule every waiting task on the executor.
   auto waitingTask = queueHead.getTask();
   while (waitingTask) {
     // Find the next waiting task.