Remove unnecessary full-subtree layouts for filtered SVG containers

Remove unnecessary full-subtree layouts for filtered SVG containers

The presence of a filter on a container (or the SVG root) would force
a layout of the entire subtree if any child needed a layout. This used
to serve the purpose of making sure that the entire subtree would get
repainted (an artifact of how 'filter' is handled on SVG elements.)
With the current paint invalidation system, this should however make
no practical difference, since the layout of the subtree will only
end up marking descendant LayoutObjects as "maybe needing paint
invalidation" - which the ones that didn't actually change don't - and
hence for these nothing will be invalidated.
The container itself will be invalidated via the call to
SVGResourcesCache::clientLayoutChanged, which will mark it for paint
invalidation if it has instantiated a filter resource.

BUG=603956
Committed: https://crrev.com/b6a48975dfe23cf5721c0712052057112055cabb
Cr-Commit-Position: refs/heads/master@{#389283}

[fs, 2016-04-22 15:48:27]

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

[fs, 2016-04-22 15:48:28]

Now I've managed to convince myself (by tests and code-stepping) that these
conditions are not useful (rather somewhat harmful), so now you get a chance to
convince me otherwise.

[pdr., 2016-04-22 22:47:41]

On 2016/04/22 at 15:48:28, fs wrote:
> Now I've managed to convince myself (by tests and code-stepping) that these
conditions are not useful (rather somewhat harmful), so now you get a chance to
convince me otherwise.

It looks like this was added by my friend Joel Webber many moons ago:
https://bugs.webkit.org/show_bug.cgi?id=71733. This case should definitely be
handled by paint invalidation which didn't really work back then.

LGTM!

[fs, 2016-04-22 22:54:36]

The CQ bit was checked by fs@opera.com

[commit-bot: I haz the power, 2016-04-22 22:55:22]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1907273002/20001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1907273002/20001

[commit-bot: I haz the power, 2016-04-22 23:00:16]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2016-04-22 23:01:45]

Description was changed from

==========
Remove unnecessary full-subtree layouts for filtered SVG containers

The presence of a filter on a container (or the SVG root) would force
a layout of the entire subtree if any child needed a layout. This used
to serve the purpose of making sure that the entire subtree would get
repainted (an artifact of how 'filter' is handled on SVG elements.)
With the current paint invalidation system, this should however make
no practical difference, since the layout of the subtree will only
end up marking descendant LayoutObjects as "maybe needing paint
invalidation" - which the ones that didn't actually change don't - and
hence for these nothing will be invalidated.
The container itself will be invalidated via the call to
SVGResourcesCache::clientLayoutChanged, which will mark it for paint
invalidation if it has instantiated a filter resource.

BUG=603956
==========

to

==========
Remove unnecessary full-subtree layouts for filtered SVG containers

The presence of a filter on a container (or the SVG root) would force
a layout of the entire subtree if any child needed a layout. This used
to serve the purpose of making sure that the entire subtree would get
repainted (an artifact of how 'filter' is handled on SVG elements.)
With the current paint invalidation system, this should however make
no practical difference, since the layout of the subtree will only
end up marking descendant LayoutObjects as "maybe needing paint
invalidation" - which the ones that didn't actually change don't - and
hence for these nothing will be invalidated.
The container itself will be invalidated via the call to
SVGResourcesCache::clientLayoutChanged, which will mark it for paint
invalidation if it has instantiated a filter resource.

BUG=603956

Committed: https://crrev.com/b6a48975dfe23cf5721c0712052057112055cabb
Cr-Commit-Position: refs/heads/master@{#389283}
==========

[commit-bot: I haz the power, 2016-04-22 23:01:47]

Patchset 2 (id:??) landed as
https://crrev.com/b6a48975dfe23cf5721c0712052057112055cabb
Cr-Commit-Position: refs/heads/master@{#389283}