Use platform implementation of Monitor in thread pool

runtime/bin/thread_pool_win.cc

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "bin/thread_pool.h"
 
-TaskQueue::TaskQueue() : terminate_(false), head_(NULL), tail_(NULL) {
-  UNIMPLEMENTED();
-}
-
-
-void TaskQueue::Insert(TaskQueueEntry* entry) {
-  UNIMPLEMENTED();
-}
-
-
-void TaskQueue::Shutdown() {
-  UNIMPLEMENTED();
-}
-
-
-TaskQueueEntry* TaskQueue::Remove() {
-  UNIMPLEMENTED();
-  return NULL;
-}
-
-
 void ThreadPool::Start() {
   UNIMPLEMENTED();
 }
 
 
 void ThreadPool::Shutdown() {
   UNIMPLEMENTED();
 }