Mojo + GN: Fix missing dependencies in existing existing mojom targets.

mojo/services/public/interfaces/input_events/BUILD.gn

 # 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.
 
 import("//mojo/public/tools/bindings/mojom.gni")
 
 # GYP version: mojo/mojo_services.gypi:mojo_input_events_bindings
 mojom("input_events") {
   sources = [
     "input_events.mojom",
+    "input_event_constants.mojom",
+    "input_key_codes.mojom",
   ]
 
   deps = [
     "//mojo/services/public/interfaces/geometry",
   ]
 }