Add Media device notification to SystemMonitor and Mac impl

base/system_monitor/mock_devices_changed_observer.cc

Index: base/system_monitor/mock_devices_changed_observer.cc
diff --git a/base/system_monitor/mock_devices_changed_observer.cc b/base/system_monitor/mock_devices_changed_observer.cc
new file mode 100644
index 0000000000000000000000000000000000000000..ab3c7f4fac80e2aa6ee1fd3448fe073f908e3f3c
--- /dev/null
+++ b/base/system_monitor/mock_devices_changed_observer.cc
@@ -0,0 +1,19 @@
+// Copyright (c) 2012 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 "base/system_monitor/mock_devices_changed_observer.h"
+
+#include "base/file_path.h"
+
+namespace base {
+namespace test {
+
+MockDevicesChangedObserver::MockDevicesChangedObserver() {
+}
+
+MockDevicesChangedObserver::~MockDevicesChangedObserver() {
+}
+
+}  // namespace test
+}  // namespace base