Scanner: Fix bug and add coverage for iterators/generators.

* Fix bad function call in Context. This bug was not found before
  because it only shows up when trying to report an error on this
  type of scan context.
* Coverage/fixes for iterator.next() and *IteratorPrototype.
* Coverage/fixes for generators.
* Add missing coverage for DOMSettableTokenList.

@ a6049ae44f72e5b5de7216bd7c64ec29c5c0e237

[felix8a, 2016-04-28 19:43:52]

lgtm.

meta-comment: I've already forgotten most of what I know about the scanner, and
I'm not finding it easy to reconstruct that understanding, so this is just a
fairly superficial review. The changes locally seem to make sense, and I'm
trusting that you understand the implications of the change better than me.

If you'd like me to do a deeper review, I can find some time tomorrow.

[kpreid_google, 2016-04-28 19:52:00]

On 2016/04/28 19:43:52, felix8a wrote:
> lgtm.
> 
> meta-comment: I've already forgotten most of what I know about the scanner,
and
> I'm not finding it easy to reconstruct that understanding, so this is just a
> fairly superficial review. The changes locally seem to make sense, and I'm
> trusting that you understand the implications of the change better than me.

“Everyone knows that debugging is twice as hard as writing a program in the
first place. So if you're as clever as you can be when you write it, how will
you ever debug it?”

I'm fairly confident that this change is a strict improvement. It introduces a
kludge (the pseudo-ctors) but everything else is straightforward, and the kludge
is less “clever” than my attempt to make Context directly understand the
iterator prototypes.

[kpreid_google, 2016-04-28 22:01:37]

* Fix bad function call in Context. This bug was not found before
  because it only shows up when trying to report an error on this
  type of scan context.
* Coverage/fixes for iterator.next() and *IteratorPrototype.
* Coverage/fixes for generators.
* Add missing coverage for DOMSettableTokenList.

[kpreid_google, 2016-04-28 22:03:24]

New snapshot just moves a function declaration to where it needs to be to obey
ES5 strict rules (which Chrome has moved on from but Firefox hasn't yet).

[MarkM, 2016-04-28 22:06:17]

still LGTM

[MarkM, 2016-04-28 22:06:47]

On 2016/04/28 22:06:17, MarkM wrote:
> still LGTM

Oops. wrong cl. nevermind

[felix8a, 2016-04-29 06:00:01]

lgtm