sync: Gracefully handle very early shutdown

sync/internal_api/public/base/cancellation_observer.cc

Index: sync/internal_api/public/base/cancellation_observer.cc
diff --git a/sync/internal_api/public/base/cancellation_observer.cc b/sync/internal_api/public/base/cancellation_observer.cc
new file mode 100644
index 0000000000000000000000000000000000000000..7b396b575f2fd75aa808303bd786731785502633
--- /dev/null
+++ b/sync/internal_api/public/base/cancellation_observer.cc
@@ -0,0 +1,13 @@
+// Copyright (c) 2013 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/cancellation_observer.h"
+
+namespace syncer {
+
+CancellationObserver::CancellationObserver() {}
+
+CancellationObserver::~CancellationObserver() {}
+
+}  // namespace syncer