Fix more warnings for dart:html.

tools/dom/scripts/htmlrenamer.py

 #!/usr/bin/python
 # Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 # for details. All rights reserved. Use of this source code is governed by a
 # BSD-style license that can be found in the LICENSE file.
 import logging
 import monitored
 import re
 
 typed_array_renames = {
     'ArrayBuffer': 'ByteBuffer',
@@ skipping 735 matching lines @@
     'Performance.webkitGetEntries',
     'Performance.webkitGetEntriesByName',
     'Performance.webkitGetEntriesByType',
     'Performance.webkitMark',
     'Performance.webkitMeasure',
     'ShadowRoot.getElementsByTagNameNS',
     'SVGElement.getPresentationAttribute',
     'SVGElementInstance.on:wheel',
     'WheelEvent.wheelDelta',
     'Window.on:wheel',
+    'WindowEventHandlers.on:beforeUnload',
     'WorkerGlobalScope.webkitIndexedDB',
 # TODO(jacobr): should these be removed?
     'Document.close',
     'Document.hasFocus',
     ])
 
 # Manual dart: library name lookup.
 _library_names = monitored.Dict('htmlrenamer._library_names', {
   'ANGLEInstancedArrays': 'web_gl',
   'Database': 'web_sql',
@@ skipping 197 matching lines @@
 
     # We're looking for a sequence of letters which start with capital letter
     # then a series of caps and finishes with either the end of the string or
     # a capital letter.
     # The [0-9] check is for names such as 2D or 3D
     # The following test cases should match as:
     #   WebKitCSSFilterValue: WebKit(C)(SS)(F)ilterValue
     #   XPathNSResolver: (X)()(P)ath(N)(S)(R)esolver (no change)
     #   IFrameElement: (I)()(F)rameElement (no change)
     return re.sub(r'([A-Z])([A-Z]{2,})([A-Z]|$)', toLower, name)