Add SVGUseElement::createInstanceTree helper

Add SVGUseElement::createInstanceTree helper

Add a new method used to create a new instance subtree from a <use>-
targetted element. Re-use where possible.

Also make isDisallowedElement(...) take a Element& (it's no longer
called on Nodes) and remove a redundant call to
removeDisallowedElementsFromSubtree in <symbol> expansion (no new clones
are produced here expecpt the <svg> on replacing the <symbol>.)

BUG=589682
Committed: https://crrev.com/8a99876d324ea81915ad034e351c3154e77e43ba
Cr-Commit-Position: refs/heads/master@{#379298}

[fs, 2016-03-04 15:56:24]

fs@opera.com changed reviewers:
+ pdr@chromium.org, schenney@chromium.org

[Stephen Chennney, 2016-03-04 16:00:16]

LGTM

[fs, 2016-03-04 16:18:23]

The CQ bit was checked by fs@opera.com

[commit-bot: I haz the power, 2016-03-04 16:18:43]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1763033002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1763033002/1

[commit-bot: I haz the power, 2016-03-04 16:23:54]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2016-03-04 16:25:26]

Description was changed from

==========
Add SVGUseElement::createInstanceTree helper

Add a new method used to create a new instance subtree from a <use>-
targetted element. Re-use where possible.

Also make isDisallowedElement(...) take a Element& (it's no longer
called on Nodes) and remove a redundant call to
removeDisallowedElementsFromSubtree in <symbol> expansion (no new clones
are produced here expecpt the <svg> on replacing the <symbol>.)

BUG=589682
==========

to

==========
Add SVGUseElement::createInstanceTree helper

Add a new method used to create a new instance subtree from a <use>-
targetted element. Re-use where possible.

Also make isDisallowedElement(...) take a Element& (it's no longer
called on Nodes) and remove a redundant call to
removeDisallowedElementsFromSubtree in <symbol> expansion (no new clones
are produced here expecpt the <svg> on replacing the <symbol>.)

BUG=589682

Committed: https://crrev.com/8a99876d324ea81915ad034e351c3154e77e43ba
Cr-Commit-Position: refs/heads/master@{#379298}
==========

[commit-bot: I haz the power, 2016-03-04 16:25:27]

Patchset 1 (id:??) landed as
https://crrev.com/8a99876d324ea81915ad034e351c3154e77e43ba
Cr-Commit-Position: refs/heads/master@{#379298}