Do nothing on OnSessionStopped if ARC is being restarted.

components/arc/arc_stop_reason.h

Index: components/arc/arc_stop_reason.h
diff --git a/components/arc/arc_stop_reason.h b/components/arc/arc_stop_reason.h
new file mode 100644
index 0000000000000000000000000000000000000000..df104439e7a3eea8861ed9d683c68665b3f590c2
--- /dev/null
+++ b/components/arc/arc_stop_reason.h
@@ -0,0 +1,34 @@
+// Copyright 2017 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.
+
+#ifndef COMPONENTS_ARC_ARC_STOP_REASON_H_
+#define COMPONENTS_ARC_ARC_STOP_REASON_H_
+
+#include <ostream>
+
+namespace arc {
+
+// Describes the reason the ARC instance is stopped.
+enum class ArcStopReason {
+  // ARC instance has been gracefully shut down.
+  SHUTDOWN,
+
+  // Errors occurred during the ARC instance boot. This includes any failures
+  // before the instance is actually attempted to be started, and also
+  // failures on bootstrapping IPC channels with Android.
+  GENERIC_BOOT_FAILURE,
+
+  // The device is critically low on disk space.
+  LOW_DISK_SPACE,
+
+  // ARC instance has crashed.
+  CRASH,
+};
+
+// Defines "<<" operator for LOGging purpose.
+std::ostream& operator<<(std::ostream& os, ArcStopReason reason);
+
+}  // namespace arc
+
+#endif  // COMPONENTS_ARC_ARC_STOP_REASON_H_