Change the thread interface in runtime/platform and use it starting all threads

runtime/bin/thread_pool_win.cc

Index: runtime/bin/thread_pool_win.cc
diff --git a/runtime/bin/thread_pool_win.cc b/runtime/bin/thread_pool_win.cc
deleted file mode 100644
index cf6b860e76b44c0f80afe4857fe8c0e39dc413a3..0000000000000000000000000000000000000000
--- a/runtime/bin/thread_pool_win.cc
+++ /dev/null
@@ -1,14 +0,0 @@
-// 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"
-
-void ThreadPool::Start() {
-  UNIMPLEMENTED();
-}
-
-
-void ThreadPool::Shutdown() {
-  UNIMPLEMENTED();
-}