Refactor ModelTypePayloadMap and ObjectIdPayloadMap to StateMaps.

sync/notifier/invalidation_util.cc

Index: sync/notifier/invalidation_util.cc
diff --git a/sync/notifier/invalidation_util.cc b/sync/notifier/invalidation_util.cc
index b10e2b498b2d29d204c4a82ee84ed4e6a29c1b90..7307292d4c7044c8be392783cefeef55a05f21a2 100644
--- a/sync/notifier/invalidation_util.cc
+++ b/sync/notifier/invalidation_util.cc
@@ -4,11 +4,18 @@
 
 #include "sync/notifier/invalidation_util.h"
 
+#include <ostream>
 #include <sstream>
 
 #include "google/cacheinvalidation/include/types.h"
 #include "google/cacheinvalidation/types.pb.h"
 
+namespace invalidation {
+void PrintTo(const invalidation::ObjectId& id, std::ostream* os) {
+  *os << syncer::ObjectIdToString(id);
+}
+}  // namespace invalidation
+
 namespace syncer {
 
 bool ObjectIdLessThan::operator()(const invalidation::ObjectId& lhs,