Introduce a layering in the invalidation component as public and impl

components/invalidation/ack_handler.cc

Index: components/invalidation/ack_handler.cc
diff --git a/components/invalidation/ack_handler.cc b/components/invalidation/ack_handler.cc
deleted file mode 100644
index 68dc028092a0bd3c8853ee620bd8beaccbdeae98..0000000000000000000000000000000000000000
--- a/components/invalidation/ack_handler.cc
+++ /dev/null
@@ -1,17 +0,0 @@
-// Copyright 2014 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.
-
-#include "components/invalidation/ack_handler.h"
-
-#include "components/invalidation/invalidation.h"
-
-namespace syncer {
-
-AckHandler::AckHandler() {
-}
-
-AckHandler::~AckHandler() {
-}
-
-}  // namespace syncer