Devirtualize Document class type checking

Devirtualize Document class type checking

Document has a bunch of virtual bool is*Document() methods on it, but it also has
two bools for XHTML and HTML documents which is silly. We can merge them all
together into an enum of values and devirtualize the type checking methods.

This patch introduces the DocumentClass enum that is used to signal what subclass
of Document, or HTMLDocument, is being implemented.

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=149828

[abarth-chromium, 2013-05-06 23:26:46]

lgtm

ok

[eseidel, 2013-05-06 23:28:30]

Eh. Seems OK.  I'm not sure why the bools existed in the first place. 
Historically we've added storage for this sort of thing when speed is important.
 I doubt speed matters much here.

[esprehn, 2013-05-06 23:40:00]

isHTMLDocument is called in a bunch of performance critical places (ex. CSS
parsing) so I understand wanting that to be non-virtual. The bool for XHTML is
needed so we can tell if createElement should return HTMLElement instances in
Document since there's no XHTMLDocument class. This just seemed like a nice
unification of all the type checking things instead of having the two bools for
those things and then lots of virtual methods for the other ones.

[arv (Not doing code reviews), 2013-05-06 23:59:25]

LGTM

Does this impact performance?

[esprehn, 2013-05-07 00:07:08]

On 2013/05/06 23:59:25, arv wrote:
> LGTM
> 
> Does this impact performance?

The ones that would be critical are already non-virtual I think, and I can't
imagine an & operation is going to impact performance. We've added lots of bit
fiddling in the tree and never noticed it (ex. masked DOM wrapper ptrs).

[commit-bot: I haz the power, 2013-05-07 00:11:07]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/esprehn@chromium.org/14839007/3001

[commit-bot: I haz the power, 2013-05-07 00:47:00]

Change committed as 149828