Add struct_traits and typemap for blink::WebGamepad

device/gamepad/public/interfaces/gamepad_typemapping_test.mojom

Index: device/gamepad/public/interfaces/gamepad_typemapping_test.mojom
diff --git a/device/gamepad/public/interfaces/gamepad_typemapping_test.mojom b/device/gamepad/public/interfaces/gamepad_typemapping_test.mojom
new file mode 100644
index 0000000000000000000000000000000000000000..bb7d28e490fe46488c3e99e0c39aad9b14605a9d
--- /dev/null
+++ b/device/gamepad/public/interfaces/gamepad_typemapping_test.mojom
@@ -0,0 +1,11 @@
+// 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.
+
+module device.mojom;
+
+import "device/gamepad/public/interfaces/gamepad.mojom";
+
+interface GamepadTypeMappingTest {
+  PassGamepad(Gamepad send) => (Gamepad echo);
+};