[SVG] Skip layout viewport change calculation when not needed.

[SVG] Skip layout viewport change calculation when not needed.

SVGRenderSupport::layoutChildren() determines whether the size of the
nearest viewport has changed upfront, and then uses this information to
force a re-layout of relative-length children.

But the relative-length flag is always propagated up the ancestor chain
(see SVGElement::updateRelativeLengthsInformation), so we can
immediately tell whether there are any relative-length descendants. If
there aren't, we can skip the viewport change crawl and related logic.

R=pdr@chromium.org,schenney@chromium.org,fs@opera.com,ed@opera.com

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=180071

[kouhei (in TOK), 2014-08-10 15:56:16]

lgtm

[f(malita), 2014-08-10 16:15:38]

Actually, I think we can drop the forced resource inval of non-rel children
altogether -- it is now handled by
SVGElement::invalidateRelativeLengthClients()!

PTAL

(I'll also add a new test just to be sure, although I suspect there's plenty of
coverage)

[pdr., 2014-08-10 20:44:45]

On 2014/08/10 16:15:38, Florin Malita wrote:
> Actually, I think we can drop the forced resource inval of non-rel children
> altogether -- it is now handled by
> SVGElement::invalidateRelativeLengthClients()!
> 
> PTAL
> 
> (I'll also add a new test just to be sure, although I suspect there's plenty
of
> coverage)

Nice! LGTM

[f(malita), 2014-08-12 13:34:11]

The CQ bit was checked by fmalita@chromium.org

[commit-bot: I haz the power, 2014-08-12 13:35:21]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/fmalita@chromium.org/458833002/40001

[commit-bot: I haz the power, 2014-08-12 13:41:09]

Change committed as 180071