Decouple content transform fiddling from SVGRenderingContext::renderSubtree

Decouple content transform fiddling from SVGRenderingContext::renderSubtree

The "content transform" is essentially a property of the call-site, and
is hence invariant for a sequence of calls to renderSubtree.
This means we ought to be able to save-mutate-restore (SMR) once per
call-site, and not per call to renderSubtree. Achieve this by moving the
SMR to a helper SubtreeContentTransformScope, and then instantiate objects
where needed.
This means the transform-logistics can be cleaned up a bit for some of the
callers.

BUG=420022
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=184245

[fs, 2014-10-22 15:21:43]

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

[fs, 2014-10-22 15:21:44]

@fmalita: Since we touched upon the contentTransform in the DL-pattern review, I
hacked this up? At least makes for better grep-ability =) WDYT?

[f(malita), 2014-10-22 17:44:47]

On 2014/10/22 15:21:44, fs wrote:
> @fmalita: Since we touched upon the contentTransform in the DL-pattern review,
I
> hacked this up? At least makes for better grep-ability =) WDYT?

LGTM, thanks!

[fs, 2014-10-23 08:35:24]

The CQ bit was checked by fs@opera.com

[commit-bot: I haz the power, 2014-10-23 08:36:37]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/666403002/1

[commit-bot: I haz the power, 2014-10-23 08:40:59]

Committed patchset #1 (id:1) as 184245