sync: Inject sync/'s dependency on invalidations

sync/internal_api/public/base/invalidation_interface.cc

Index: sync/internal_api/public/base/invalidation_interface.cc
diff --git a/sync/internal_api/public/base/invalidation_interface.cc b/sync/internal_api/public/base/invalidation_interface.cc
new file mode 100644
index 0000000000000000000000000000000000000000..0284170837858e07cc2469aa0869f9a850a6c72f
--- /dev/null
+++ b/sync/internal_api/public/base/invalidation_interface.cc
@@ -0,0 +1,29 @@
+// 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 "sync/internal_api/public/base/invalidation_interface.h"
+
+namespace syncer {
+
+bool InvalidationInterface::LessThanByVersion(const InvalidationInterface& a,
+                                              const InvalidationInterface& b) {
+  if (a.IsUnknownVersion() && !b.IsUnknownVersion())
+    return true;
+
+  if (!a.IsUnknownVersion() && b.IsUnknownVersion())
+    return false;
+
+  if (a.IsUnknownVersion() && b.IsUnknownVersion())
+    return false;
+
+  return a.GetVersion() < b.GetVersion();
+}
+
+InvalidationInterface::InvalidationInterface() {
+}
+
+InvalidationInterface::~InvalidationInterface() {
+}
+
+}  // namespace syncer