Introduce a layering in the invalidation component as public and impl

components/invalidation/base/single_object_invalidation_set.cc

Index: components/invalidation/base/single_object_invalidation_set.cc
diff --git a/components/invalidation/single_object_invalidation_set.cc b/components/invalidation/base/single_object_invalidation_set.cc
similarity index 95%
rename from components/invalidation/single_object_invalidation_set.cc
rename to components/invalidation/base/single_object_invalidation_set.cc
index c05c517eeeeb6d641ffee8eea669b2acb1207e74..2e5b777ce43d94f17f4dfffb0e3348fe6376b9ab 100644
--- a/components/invalidation/single_object_invalidation_set.cc
+++ b/components/invalidation/base/single_object_invalidation_set.cc
@@ -2,10 +2,10 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#include "components/invalidation/single_object_invalidation_set.h"
+#include "components/invalidation/base/single_object_invalidation_set.h"
 
 #include "base/values.h"
-#include "components/invalidation/invalidation_util.h"
+#include "components/invalidation/base/invalidation_util.h"
 
 namespace syncer {