Add missing header files to GN files (2 of N)

third_party/WebKit/Source/core/events/BUILD.gn

 # 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.
 
 import("//third_party/WebKit/Source/core/core.gni")
 
 blink_core_sources("events") {
   sources = [
     "AddEventListenerOptionsDefaults.h",
     "AddEventListenerOptionsResolved.cpp",
@@ skipping 14 matching lines @@
     "CompositionEvent.h",
     "CustomEvent.cpp",
     "CustomEvent.h",
     "DOMWindowEventQueue.cpp",
     "DOMWindowEventQueue.h",
     "DragEvent.cpp",
     "DragEvent.h",
     "ErrorEvent.cpp",
     "ErrorEvent.h",
     "Event.cpp",
+    "Event.h",
     "EventDispatchMediator.cpp",
     "EventDispatchMediator.h",
     "EventDispatchResult.h",
     "EventDispatcher.cpp",
     "EventDispatcher.h",
     "EventFactory.h",
     "EventListener.h",
     "EventListenerMap.cpp",
     "EventListenerMap.h",
     "EventPath.cpp",
@@ skipping 69 matching lines @@
     "WheelEvent.h",
     "WindowEventContext.cpp",
     "WindowEventContext.h",
   ]
 
   configs += [
     # TODO(jschuh): crbug.com/167187 fix size_t to int truncations.
     "//build/config/compiler:no_size_t_to_int_warning",
   ]
 }