Avoid cache when deprecating document.all

chrome/renderer/resources/extensions/platform_app.js

 // Copyright (c) 2012 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.
 
 var forEach = require('utils').forEach;
 
 /**
  * Returns a function that throws a 'not available' exception when called.
  *
  * @param {string} messagePrefix text to prepend to the exception message.
@@ skipping 99 matching lines @@
 // point to the page's document (it will be reset between now and then).
 // We can't listen for the "readystatechange" event on the document (because
 // the object that it's dispatched on doesn't exist yet), but we can instead
 // do it at the window level in the capturing phase.
 window.addEventListener('readystatechange', function(event) {
   if (document.readyState != 'loading')
     return;
 
   // Deprecated document properties from
   // https://developer.mozilla.org/en/DOM/document.
+  // To deprecate document.all, simply changing its getter and setter would
+  // activate its cache mechanism, and degrade the performance. Here we assign
+  // it first to 'undefined' to avoid this.
+  document.all = undefined;

[not at google - send to devlin, 2013/05/29 15:58:05]

is this the only property that will ever suffer from that problem? if not, it
makes sense to move this into disableGetters.

otherwise lgtm.

[miket_OOO, 2013/05/29 16:19:14]

Ben, I'm probably misreading disableGetters (which is a helper I'm not familiar
with), but isn't document.all already there in line 125?

[not at google - send to devlin, 2013/05/29 16:24:31]

I mean make disableGetters assign every property to undefined ('document',
'aLinkColor', 'all', etc) before setting the getter, rather than only doing it
for document.all.

   disableGetters(document, 'document',
       ['alinkColor', 'all', 'bgColor', 'fgColor', 'linkColor',
        'vlinkColor']);
 }, true);
 
 // Disable onunload, onbeforeunload.
 Window.prototype.__defineSetter__(
     'onbeforeunload', generateDisabledMethodStub('onbeforeunload'));
 Window.prototype.__defineSetter__(
     'onunload', generateDisabledMethodStub('onunload'));
 var windowAddEventListener = Window.prototype.addEventListener;
 Window.prototype.addEventListener = function(type) {
   if (type === 'unload' || type === 'beforeunload')
     generateDisabledMethodStub(type)();
   else
     return windowAddEventListener.apply(window, arguments);
 };