Implement features needed for local ack handling in InvalidationStateTracker.

sync/notifier/p2p_invalidator_unittest.cc

Index: sync/notifier/p2p_invalidator_unittest.cc
diff --git a/sync/notifier/p2p_invalidator_unittest.cc b/sync/notifier/p2p_invalidator_unittest.cc
index 6be2c218098a705384caf8b018953ea7fc2044e8..bb0d3c2df3339cd2d83b73b9a1919ed3dde288e8 100644
--- a/sync/notifier/p2p_invalidator_unittest.cc
+++ b/sync/notifier/p2p_invalidator_unittest.cc
@@ -194,9 +194,9 @@ TEST_F(P2PInvalidatorTest, P2PNotificationDataNonDefault) {
   EXPECT_EQ(
       "{\"idInvalidationMap\":["
       "{\"objectId\":{\"name\":\"BOOKMARK\",\"source\":1004},"
-      "\"state\":{\"ackHandle\":{},\"payload\":\"\"}},"
+      "\"state\":{\"ackHandle\":{\"state\":\"\"},\"payload\":\"\"}},"
       "{\"objectId\":{\"name\":\"THEME\",\"source\":1004},"
-      "\"state\":{\"ackHandle\":{},\"payload\":\"\"}}"
+      "\"state\":{\"ackHandle\":{\"state\":\"\"},\"payload\":\"\"}}"
       "],\"notificationType\":\"notifyAll\","
       "\"senderId\":\"sender\",\"source\":1}", notification_data_str);