Remove most of WebDOMEvent and delete WebDOMMouseEvent.

third_party/WebKit/Source/web/web.gypi

 {
   'variables': {
     'web_files': [
       'AssertMatchingEnums.cpp',
       'AssociatedURLLoader.cpp',
       'AssociatedURLLoader.h',
       'ChromeClientImpl.cpp',
       'ChromeClientImpl.h',
       'ColorChooserPopupUIController.cpp',
       'ColorChooserPopupUIController.h',
@@ skipping 105 matching lines @@
       'WebCryptoNormalize.cpp',
       'WebCustomElement.cpp',
       'WebCSSParser.cpp',
       'WebDOMActivityLogger.cpp',
       'WebDOMCustomEvent.cpp',
       'WebDOMError.cpp',
       'WebDOMEvent.cpp',
       'WebDOMFileSystem.cpp',
       'WebDOMMediaStreamTrack.cpp',
       'WebDOMMessageEvent.cpp',
-      'WebDOMMouseEvent.cpp',
       'WebDOMProgressEvent.cpp',
       'WebDOMResourceProgressEvent.cpp',
       'WebDataSourceImpl.cpp',
       'WebDataSourceImpl.h',
       'WebDatabase.cpp',
       'WebDateTimeSuggestion.cpp',
       'WebDevToolsAgentImpl.cpp',
       'WebDevToolsAgentImpl.h',
       'WebDevToolsFrontendImpl.cpp',
       'WebDevToolsFrontendImpl.h',
@@ skipping 196 matching lines @@
         {
           'web_unittest_files': [
             # Mac uses ScrollAnimatorMac instead of ScrollAnimatorNone.
             'tests/ScrollAnimatorNoneTest.cpp',
           ],
         }
       ],
     ],
   },
 }