Implement features needed for local ack handling in InvalidationStateTracker.

sync/internal_api/public/base/invalidation_test_util.h

Index: sync/internal_api/public/base/invalidation_test_util.h
diff --git a/sync/internal_api/public/base/invalidation_test_util.h b/sync/internal_api/public/base/invalidation_test_util.h
index 694081d3fb35f036100467d02dcfd418efbdcba8..970db8ae6afc6cac75d1255324f607ce230a663a 100644
--- a/sync/internal_api/public/base/invalidation_test_util.h
+++ b/sync/internal_api/public/base/invalidation_test_util.h
@@ -11,8 +11,13 @@
 
 namespace syncer {
 
+class AckHandle;
 struct Invalidation;
 
+void PrintTo(const AckHandle& ack_handle, ::std::ostream* os);
+::testing::Matcher<const AckHandle&> Eq(
+    const AckHandle& expected);
+
 void PrintTo(const Invalidation& invalidation, ::std::ostream* os);
 
 ::testing::Matcher<const Invalidation&> Eq(const Invalidation& expected);