Mojo: Add the ability to hook up a channel to the embedder API.

mojo/system/test_embedder.h

+// Copyright 2014 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 MOJO_SYSTEM_TEST_EMBEDDER_H_
+#define MOJO_SYSTEM_TEST_EMBEDDER_H_
+
+namespace mojo {
+namespace embedder {
+namespace test {
+
+// This shuts down the global, singleton instance. (Note: "Real" embedders are
+// not expected to ever shut down this instance. This |Shutdown()| function will
+// do more work to ensure that tests don't leak, etc.)
+// TODO(vtl): Figure out the library/component/DLL/export situation for test
+// embedder stuff. For now, it's linked directly into the unit test binary.
+void Shutdown();
+
+}  // namespace test
+}  // namespace embedder
+}  // namespace mojo
+
+#endif  // MOJO_SYSTEM_EMBEDDER_H_