Use element.classList if available to speed up class manipulation

[spasche]

Element.classList is a new API introduced in HTML5 for manipulating the classes of an element. The API is documented on ​https://developer.mozilla.org/en/DOM/element.classList.

This API is implemented in Firefox 3.6 and WebKit is planning to implement it.

Dojo could detect if this property is available and use it in the {add,had,remove,toggle}Class functions. A 2-40 speedup could be achieved with Firefox according to this benchmark: ​https://bug501257.bugzilla.mozilla.org/attachment.cgi?id=395627).

[Eugene Lazutkin]

Done in [25704] of #9641.

[bill]

See also duplicate ticket #11465.

[Eugene Lazutkin]

It was reverted in [25745]. We decided to postpone it for now until vendors will ship better/faster implementations.