Introduce a layering in the invalidation component as public and impl

components/invalidation/base/ack_handler.h

Index: components/invalidation/base/ack_handler.h
diff --git a/components/invalidation/ack_handler.h b/components/invalidation/base/ack_handler.h
similarity index 82%
rename from components/invalidation/ack_handler.h
rename to components/invalidation/base/ack_handler.h
index 0a2f642bb77e166a7e98a4990bae94c323081a46..fb0c0f26391952efe61b4ed424c881b837e32172 100644
--- a/components/invalidation/ack_handler.h
+++ b/components/invalidation/base/ack_handler.h
@@ -2,12 +2,12 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#ifndef COMPONENTS_INVALIDATION_ACK_HANDLER_H_
-#define COMPONENTS_INVALIDATION_ACK_HANDLER_H_
+#ifndef COMPONENTS_INVALIDATION_BASE_ACK_HANDLER_H_
+#define COMPONENTS_INVALIDATION_BASE_ACK_HANDLER_H_
 
 #include <vector>
 
-#include "components/invalidation/invalidation_export.h"
+#include "components/invalidation/base/invalidation_export.h"
 
 namespace invalidation {
 class ObjectId;
@@ -37,4 +37,4 @@ class INVALIDATION_EXPORT AckHandler {
 
 }  // namespace syncer
 
-#endif  // COMPONENTS_INVALIDATION_ACK_HANDLER_H_
+#endif  // COMPONENTS_INVALIDATION_BASE_ACK_HANDLER_H_