Implement Invalidator::Acknowledge

sync/internal_api/public/util/weak_handle.cc

Index: sync/internal_api/public/util/weak_handle.cc
diff --git a/sync/internal_api/public/util/weak_handle.cc b/sync/internal_api/public/util/weak_handle.cc
index e6411ee4c40ebe232784bfc672125afd435f97da..ddec6db0e58fe8cefdb8ecc34fea84c60b64705c 100644
--- a/sync/internal_api/public/util/weak_handle.cc
+++ b/sync/internal_api/public/util/weak_handle.cc
@@ -31,6 +31,15 @@ void WeakHandleCoreBase::PostToOwnerThread(
   }
 }
 
+void WeakHandleCoreBase::PostWithReplyToOwnerThread(
+    const tracked_objects::Location& from_here,
+    const base::Closure& fn,
+    const base::Closure& reply) const {
+  if (!owner_loop_proxy_->PostTaskAndReply(from_here, fn, reply)) {
+    DVLOG(1) << "Could not post task from " << from_here.ToString();
+  }
+}
+
 }  // namespace internal
 
 }  // namespace syncer