[Mojo Video Capture] Stop service when last client disconnects.

services/video_capture/public/interfaces/constants.mojom

Index: services/video_capture/public/interfaces/constants.mojom
diff --git a/services/video_capture/public/interfaces/constants.mojom b/services/video_capture/public/interfaces/constants.mojom
new file mode 100644
index 0000000000000000000000000000000000000000..5ac0201c324494fb628807282c7d74a538421c8f
--- /dev/null
+++ b/services/video_capture/public/interfaces/constants.mojom
@@ -0,0 +1,8 @@
+// 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.
+
+module video_capture.mojom;
+
+const string kServiceName = "video_capture";
+const float kDefaultShutdownDelayInSeconds = 5;