Creates BackgroundShell and uses it in test

ui/views/mus/run_all_unittests_mus.cc

Index: ui/views/mus/run_all_unittests_mus.cc
diff --git a/ui/views/mus/run_all_unittests_mus.cc b/ui/views/mus/run_all_unittests_mus.cc
new file mode 100644
index 0000000000000000000000000000000000000000..4de8cdb1839a8f7617ce22c6454472e5c200eec0
--- /dev/null
+++ b/ui/views/mus/run_all_unittests_mus.cc
@@ -0,0 +1,9 @@
+// Copyright 2016 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 "ui/views/run_all_unittests.h"
+
+int MasterProcessMain(int argc, char** argv) {
+  return views::RunAllUnittests(argc, argv);
+}