Avoid cache when deprecating document.all

chrome/renderer/resources/extensions/platform_app.js

Index: chrome/renderer/resources/extensions/platform_app.js
diff --git a/chrome/renderer/resources/extensions/platform_app.js b/chrome/renderer/resources/extensions/platform_app.js
index 28450e2a64f785cf16ee49669460f38a98e2007d..e4245afc35f67f6008bd3f5267af37fbb2c1d482 100644
--- a/chrome/renderer/resources/extensions/platform_app.js
+++ b/chrome/renderer/resources/extensions/platform_app.js
@@ -117,6 +117,10 @@ window.addEventListener('readystatechange', function(event) {
 
   // 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']);