Add WorkerPool::PostTaskAndReply and use in DHCP code.

base/threading/post_task_and_reply_impl.h

Index: base/threading/post_task_and_reply_impl.h
diff --git a/base/threading/post_task_and_reply_impl.h b/base/threading/post_task_and_reply_impl.h
new file mode 100644
index 0000000000000000000000000000000000000000..d2bbac77c4d8a2a4f6a93e34a125a48fde8873cb
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+++ b/base/threading/post_task_and_reply_impl.h
@@ -0,0 +1,43 @@
+// Copyright (c) 2011 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.
+
+// This file contains the implementation shared by
+// MessageLoopProxy::PostTaskAndReply and WorkerPool::PostTaskAndReply.
+
+#ifndef BASE_THREADING_POST_TASK_AND_REPLY_IMPL_H_
+#define BASE_THREADING_POST_TASK_AND_REPLY_IMPL_H_
+#pragma once
+
+#include "base/bind.h"
+#include "base/location.h"
+
+namespace base {
+namespace internal {
+
+// Inherit from this in a class that implements PostTask appropriately
+// for sending to a destination thread.
+//
+// Note that 'reply' will always get posted back to your current
+// MessageLoop.
+//
+// If you're looking for a concrete implementation of
+// PostTaskAndReply, you probably want base::MessageLoopProxy, or you
+// may want base::WorkerPool.
+class PostTaskAndReplyImpl {
+ public:
+  // Implementation for MessageLoopProxy::PostTaskAndReply and
+  // WorkerPool::PostTaskAndReply.
+  bool PostTaskAndReply(const tracked_objects::Location& from_here,
+                        const Closure& task,
+                        const Closure& reply);
+
+ private:
+  virtual bool PostTask(const tracked_objects::Location& from_here,
+                        const Closure& task) = 0;
+};
+
+}  // namespace internal
+}  // namespace base
+
+#endif  // BASE_THREADING_POST_TASK_AND_REPLY_IMPL_H_