Add tests for InputDevice/TouchscreenDevice StructTraits.

ui/events/BUILD.gn

Index: ui/events/BUILD.gn
diff --git a/ui/events/BUILD.gn b/ui/events/BUILD.gn
index d499a0ea9751fe97c97499ad81a2f9c975197b89..effeeb8b2119bc8187c2f8406b34b5d8df46d04a 100644
--- a/ui/events/BUILD.gn
+++ b/ui/events/BUILD.gn
@@ -385,6 +385,7 @@ test("events_unittests") {
       "blink/blink_event_util_unittest.cc",
       "blink/input_handler_proxy_unittest.cc",
       "blink/input_scroll_elasticity_controller_unittest.cc",
+      "devices/mojo/device_struct_traits_unittest.cc",
       "gestures/blink/web_gesture_curve_impl_unittest.cc",
       "ipc/latency_info_param_traits_unittest.cc",
       "mojo/struct_traits_unittest.cc",
@@ -395,6 +396,7 @@ test("events_unittests") {
       "//mojo/public/cpp/bindings",
       "//third_party/WebKit/public:blink_headers",
       "//ui/events/blink",
+      "//ui/events/devices/mojo:test_interfaces",
       "//ui/events/gestures/blink",
       "//ui/events/ipc",
       "//ui/events/mojo:test_interfaces",