Handle position:absolute candidates correctly in ScrollAnchor.

Handle position:absolute candidates correctly in ScrollAnchor.

An absolute-positioned candidate should be considered only if it would
actually scroll with the scroller (otherwise the anchoring scroll will have no
effect on it).

BUG=594873
Committed: https://crrev.com/54502dc10d4a4cf3be8d9fb89db3d2927c7bbaf9
Cr-Commit-Position: refs/heads/master@{#383361}

[skobes, 2016-03-25 04:05:57]

skobes@chromium.org changed reviewers:
+ ojan@chromium.org, ymalik@chromium.org

[ymalik, 2016-03-25 18:53:19]

https://codereview.chromium.org/1831993002/diff/1/third_party/WebKit/Source/c...
File third_party/WebKit/Source/core/layout/ScrollAnchor.cpp (right):

https://codereview.chromium.org/1831993002/diff/1/third_party/WebKit/Source/c...
third_party/WebKit/Source/core/layout/ScrollAnchor.cpp:96: return
!skippedByContainerLookup;
Sorry, could you briefly explain why if !skippedByContainerLookup then we know
that candidate moves with scroller?

[skobes, 2016-03-25 19:36:35]

https://codereview.chromium.org/1831993002/diff/1/third_party/WebKit/Source/c...
File third_party/WebKit/Source/core/layout/ScrollAnchor.cpp (right):

https://codereview.chromium.org/1831993002/diff/1/third_party/WebKit/Source/c...
third_party/WebKit/Source/core/layout/ScrollAnchor.cpp:96: return
!skippedByContainerLookup;
On 2016/03/25 18:53:19, ymalik1 wrote:
> Sorry, could you briefly explain why if !skippedByContainerLookup then we know
> that candidate moves with scroller?

This is looking for cases where the candidate's "containing block" as defined by
CSS is outside of the scroller.

For example, the containing block of a position:absolute element is the nearest
"positioned" (i.e. not static) ancestor.  LayoutObject::container will continue
walking up the DOM until it finds an ancestor that
canContainAbsolutePositionObjects().

If that ancestor is outside of the scroller, the candidate's position will not
be affected by the scroll offset.

See: https://jsbin.com/lomocu/edit?html,output

[ymalik, 2016-03-25 19:40:41]

On 2016/03/25 19:36:35, skobes wrote:
>
https://codereview.chromium.org/1831993002/diff/1/third_party/WebKit/Source/c...
> File third_party/WebKit/Source/core/layout/ScrollAnchor.cpp (right):
> 
>
https://codereview.chromium.org/1831993002/diff/1/third_party/WebKit/Source/c...
> third_party/WebKit/Source/core/layout/ScrollAnchor.cpp:96: return
> !skippedByContainerLookup;
> On 2016/03/25 18:53:19, ymalik1 wrote:
> > Sorry, could you briefly explain why if !skippedByContainerLookup then we
know
> > that candidate moves with scroller?
> 
> This is looking for cases where the candidate's "containing block" as defined
by
> CSS is outside of the scroller.
> 
> For example, the containing block of a position:absolute element is the
nearest
> "positioned" (i.e. not static) ancestor.  LayoutObject::container will
continue
> walking up the DOM until it finds an ancestor that
> canContainAbsolutePositionObjects().
> 
> If that ancestor is outside of the scroller, the candidate's position will not
> be affected by the scroll offset.
> 
> See: https://jsbin.com/lomocu/edit?html,output

Makes sense. Thanks! lgtm

[skobes, 2016-03-25 21:16:47]

The CQ bit was checked by skobes@chromium.org

[commit-bot: I haz the power, 2016-03-25 21:17:07]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1831993002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1831993002/1

[commit-bot: I haz the power, 2016-03-25 21:22:32]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2016-03-25 21:23:49]

Description was changed from

==========
Handle position:absolute candidates correctly in ScrollAnchor.

An absolute-positioned candidate should be considered only if it would
actually scroll with the scroller (otherwise the anchoring scroll will have no
effect on it).

BUG=594873
==========

to

==========
Handle position:absolute candidates correctly in ScrollAnchor.

An absolute-positioned candidate should be considered only if it would
actually scroll with the scroller (otherwise the anchoring scroll will have no
effect on it).

BUG=594873

Committed: https://crrev.com/54502dc10d4a4cf3be8d9fb89db3d2927c7bbaf9
Cr-Commit-Position: refs/heads/master@{#383361}
==========

[commit-bot: I haz the power, 2016-03-25 21:23:50]

Patchset 1 (id:??) landed as
https://crrev.com/54502dc10d4a4cf3be8d9fb89db3d2927c7bbaf9
Cr-Commit-Position: refs/heads/master@{#383361}