Remove most of WebDOMEvent and delete WebDOMMouseEvent.

third_party/WebKit/public/blink_headers.gypi

 # Copyright 2015 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.
 
 {
   'variables': {
     'blink_public_sources': [
       "platform/Platform.h",
       "platform/WebApplicationCacheHost.h",
       "platform/WebApplicationCacheHostClient.h",
@@ skipping 342 matching lines @@
       "web/WebContextMenuData.h",
       "web/WebCryptoNormalize.h",
       "web/WebCustomElement.h",
       "web/WebDOMActivityLogger.h",
       "web/WebDOMCustomEvent.h",
       "web/WebDOMError.h",
       "web/WebDOMEvent.h",
       "web/WebDOMFileSystem.h",
       "web/WebDOMMediaStreamTrack.h",
       "web/WebDOMMessageEvent.h",
-      "web/WebDOMMouseEvent.h",
       "web/WebDOMProgressEvent.h",
       "web/WebDOMResourceProgressEvent.h",
       "web/WebDataSource.h",
       "web/WebDatabase.h",
       "web/WebDateTimeChooserCompletion.h",
       "web/WebDateTimeChooserParams.h",
       "web/WebDateTimeInputType.h",
       "web/WebDateTimeSuggestion.h",
       "web/WebDevToolsAgent.h",
       "web/WebDevToolsAgentClient.h",
@@ skipping 143 matching lines @@
       "web/WebWorkerContentSettingsClientProxy.h",
       "web/default/WebRenderTheme.h",
       "web/linux/WebFontRendering.h",
       "web/mac/WebScrollbarTheme.h",
       "web/mac/WebSubstringUtil.h",
       "web/modules/notifications/WebNotificationPermissionCallback.h",
       "web/win/WebFontRendering.h",
     ],
   },
 }