Make type parameter in toDataUrl have an optional default value as per the spec.

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 202 matching lines @@
   'ElementTraversal.childElementCount',
   'ElementTraversal.firstElementChild',
   'ElementTraversal.lastElementChild',
   'Event.initEvent',
   'EventTarget.addEventListener',
   'EventTarget.removeEventListener',
   'Geolocation.clearWatch',
   'Geolocation.getCurrentPosition',
   'Geolocation.watchPosition',
   'HashChangeEvent.initHashChangeEvent',
+  'HTMLCanvasElement.toDataURL',
   'HTMLTableElement.createCaption',
   'HTMLTableElement.createTBody',
   'HTMLTableElement.createTFoot',
   'HTMLTableElement.createTHead',
   'HTMLTableElement.insertRow',
   'HTMLTableElement.rows',
   'HTMLTableElement.tBodies',
   'HTMLTableRowElement.cells',
   'HTMLTableRowElement.insertCell',
   'HTMLTableSectionElement.insertRow',
@@ skipping 615 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)