Introduce a layering in the invalidation component as public and impl

components/invalidation/public/invalidation.h

Index: components/invalidation/public/invalidation.h
diff --git a/components/invalidation/invalidation.h b/components/invalidation/public/invalidation.h
similarity index 93%
rename from components/invalidation/invalidation.h
rename to components/invalidation/public/invalidation.h
index ccc1b199e7dc3e1766976f9ec6dacc9d0ad9adfa..3a44f1944535608c6dc323c30c6e8d16f78e901b 100644
--- a/components/invalidation/invalidation.h
+++ b/components/invalidation/public/invalidation.h
@@ -2,8 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#ifndef COMPONENTS_INVALIDATION_INVALIDATION_H_
-#define COMPONENTS_INVALIDATION_INVALIDATION_H_
+#ifndef COMPONENTS_INVALIDATION_PUBLIC_INVALIDATION_H_
+#define COMPONENTS_INVALIDATION_PUBLIC_INVALIDATION_H_
 
 #include <string>
 
@@ -12,8 +12,8 @@
 #include "base/memory/weak_ptr.h"
 #include "base/sequenced_task_runner.h"
 #include "base/values.h"
-#include "components/invalidation/ack_handle.h"
-#include "components/invalidation/invalidation_export.h"
+#include "components/invalidation/public/ack_handle.h"
+#include "components/invalidation/public/invalidation_export.h"
 #include "google/cacheinvalidation/include/types.h"
 
 namespace syncer {
@@ -124,4 +124,4 @@ class INVALIDATION_EXPORT Invalidation {
 
 }  // namespace syncer
 
-#endif  // COMPONENTS_INVALIDATION_INVALIDATION_H_
+#endif  // COMPONENTS_INVALIDATION_PUBLIC_INVALIDATION_H_