Add a feature flag for the new Windows USB backend.

device/base/features.cc

Index: device/base/features.cc
diff --git a/device/base/features.cc b/device/base/features.cc
new file mode 100644
index 0000000000000000000000000000000000000000..822c0dad4c3d6d0aa75ba4a57c93a97c5cac255d
--- /dev/null
+++ b/device/base/features.cc
@@ -0,0 +1,16 @@
+// 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.
+
+#include "device/base/features.h"
+
+#include "build/build_config.h"
+
+namespace device {
+
+#if defined(OS_WIN)
+const base::Feature kNewUsbBackend{"NewUsbBackend",
+                                   base::FEATURE_DISABLED_BY_DEFAULT};
+#endif  // defined(OS_WIN)
+
+}  // namespace device