[patch] #67453/#68504 js induced crashes on disabling/enabling <link> elements

[Germain Garand]

Hi,
while I was on stylesheets,
I've worked a bit on javascript style switchers problems.

The first problem: unbalanced calls to addPendingSheet()/styleSheetLoaded() 
that cause assertion failures.
Those calls are there to ensure that an alternate sheet which has been 
explicitly enabled via a script is properly loaded.
But since ordinarily we don't wait for alternate sheets, this causes 
out-of-sync problems on stylesheet count from other places that don't expect 
them.

WebCore address this with a strange "tri-state boolean", and other 
enabledViaScript() hacks, but it still looks complicated.

So the idea: when those alternate sheets are enabled via script, they behave 
exactly like preferred stylesheets. Thus why not pretend they _are_ indeed 
preferred sheets when enabled... This pretty much solve all problems because 
preferred sheets are properly tracked, and their selection is sound (i.e: 
only one sheet among a set of alternates will be applied)

Second problem: disabled sheets were discarded from the available 
alternatives. 
I believe this is incorrect, because <link>'s "disabled" attribute is only a 
DOM extension describing if a sheet is applied or not. It's not part of HTML 
and should not have such side effect on link elements.
For reference, both Mozilla 1.5 and Opera 7 keep disabled sheets in the 
available alternatives, so that you can pick them by hand.

I have tested the attached patch[1] with all style switchers I could find [2]
and it works seemingly fine.

I'll let you review :-)
Germain

[1] includes the previous patch I sent, because they otherwise conflict... 
Dirk, was it OK?

[2] a good example being: 
http://www.meyerweb.com/eric/css/ => the "presentation" menu.

Most js style switchers are derivated from this reference implementation:
http://www.alistapart.com/articles/alternate/
e.g:
http://cnx.rice.edu/content/m11255/latest/
http://www.thinksecret.com
http://lordofthemoon.com
http://www.zeldman.com

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