Introduce a layering in the invalidation component as public and impl

components/invalidation/invalidation_export.h

Index: components/invalidation/invalidation_export.h
diff --git a/components/invalidation/invalidation_export.h b/components/invalidation/invalidation_export.h
deleted file mode 100644
index 08683bee2b3c5909ff4d0ac91bc8e7763ddcb769..0000000000000000000000000000000000000000
--- a/components/invalidation/invalidation_export.h
+++ /dev/null
@@ -1,21 +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.
-
-#ifndef COMPONENTS_INVALIDATION_INVALIDATION_EXPORT_H_
-#define COMPONENTS_INVALIDATION_INVALIDATION_EXPORT_H_
-
-// The files under components/invalidation do not currently support a shared
-// library build.  There's no point in attaching attributes to them.
-//
-// Many of the files in this directory are imports from sync/notifier, which
-// did support a shared library build.  We can use this existing set of export
-// declarations as a starting point when we prepare this directory for a shared
-// library build.
-//
-// For now, we provide dummy definitions of these tags.
-
-#define INVALIDATION_EXPORT
-#define INVALIDATION_EXPORT_PRIVATE
-
-#endif  // COMPONENTS_INVALIDATION_INVALIDATION_EXPORT_H_