Add [TypeChecking=Interface] to XSLTProcessor interface

Add [TypeChecking=Interface] to XSLTProcessor interface

Also make affected arguments (to importNode() and transformTo*()) non-
optional, like in Firefox. It makes no sense to call either function
without any of the arguments, and the previous behavior was to fail
silently in that case.

Also make the return type of transformTo*() nullable to reflect how they
are actually implemented; they currently return null on failure.

BUG=462561
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=191639

[Jens Widell, 2015-03-10 10:11:55]

jl@opera.com changed reviewers:
+ philipj@opera.com

[Jens Widell, 2015-03-10 10:11:55]

PTAL

[philipj_slow, 2015-03-10 12:09:59]

The CQ bit was checked by philipj@opera.com

[philipj_slow, 2015-03-10 12:10:00]

lgtm

[commit-bot: I haz the power, 2015-03-10 12:10:16]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/996603003/1

[Jens Widell, 2015-03-10 15:06:08]

The CQ bit was checked by jl@opera.com

[Jens Widell, 2015-03-10 15:06:08]

The patchset sent to the CQ was uploaded after l-g-t-m from philipj@opera.com
Link to the patchset: https://codereview.chromium.org/996603003/#ps40001 (title:
"update test")

[commit-bot: I haz the power, 2015-03-10 15:07:06]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/996603003/40001

[commit-bot: I haz the power, 2015-03-10 17:11:29]

Committed patchset #3 (id:40001) as
https://src.chromium.org/viewvc/blink?view=rev&revision=191639