Remove redundant check in SVGUseElement::buildShadowTree

Remove redundant check in SVGUseElement::buildShadowTree

We already perform this check on |target| in all callers (the method
itself and buildShadowAndInstanceTree), so this condition will never be
true at this point. Remove it (replace with assert.) Since this gets rid
of the only way for buildShadowTree to return false, change the return-
type to 'void' and simplify accordingly.

BUG=589682
Committed: https://crrev.com/c60a0e23cf1b1f656692ac49dbbf3aad45869722
Cr-Commit-Position: refs/heads/master@{#378504}

[fs, 2016-03-01 16:57:21]

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

[pdr., 2016-03-01 18:33:41]

On 2016/03/01 at 16:57:22, fs wrote:
> 

A++++ would review again

LGTM

[fs, 2016-03-01 18:57:38]

The CQ bit was checked by fs@opera.com

[commit-bot: I haz the power, 2016-03-01 18:58:26]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1754693002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1754693002/1

[commit-bot: I haz the power, 2016-03-01 19:08:11]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2016-03-01 19:09:14]

Description was changed from

==========
Remove redundant check in SVGUseElement::buildShadowTree

We already perform this check on |target| in all callers (the method
itself and buildShadowAndInstanceTree), so this condition will never be
true at this point. Remove it (replace with assert.) Since this gets rid
of the only way for buildShadowTree to return false, change the return-
type to 'void' and simplify accordingly.

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

to

==========
Remove redundant check in SVGUseElement::buildShadowTree

We already perform this check on |target| in all callers (the method
itself and buildShadowAndInstanceTree), so this condition will never be
true at this point. Remove it (replace with assert.) Since this gets rid
of the only way for buildShadowTree to return false, change the return-
type to 'void' and simplify accordingly.

BUG=589682

Committed: https://crrev.com/c60a0e23cf1b1f656692ac49dbbf3aad45869722
Cr-Commit-Position: refs/heads/master@{#378504}
==========

[commit-bot: I haz the power, 2016-03-01 19:09:15]

Patchset 1 (id:??) landed as
https://crrev.com/c60a0e23cf1b1f656692ac49dbbf3aad45869722
Cr-Commit-Position: refs/heads/master@{#378504}