Only allow forced fragmentainer breaks at class A break points.

Only allow forced fragmentainer breaks at class A break points.

https://drafts.csswg.org/css-break/#possible-breaks
https://drafts.csswg.org/css-break/#forced-breaks

The essential change is that forced breaks are not allowed before a first child
or after a last child, only between siblings. Floats and auto-positioned
out-of-flow siblings after the last in-flow child still need to honor the
break-after value of said last in-flow child, though.

Updated the forced-break-before-complex-margin-collapsing.html test, since it
became invalid. Top margins after forced breaks should not be eaten by the
column boundary. It also made an incorrect assumption about inserting a forced
break in front of a first child block. That's no valid class A break point.

This change also made printing/css2.1/page-break-after-003.html pass, which
has a break-after:page block with no in-flow block following it - i.e. there'll
be no class A break point for it to have any effect. It should not create a
blank page at the end.

BUG=223068, 539873
Committed: https://crrev.com/893602648192952b73b33f060d7767c51b5440ed
Cr-Commit-Position: refs/heads/master@{#385955}

[mstensho (USE GERRIT), 2016-04-05 18:05:04]

Description was changed from

==========
Only allow forced fragmentainer breaks at class A break points.

https://drafts.csswg.org/css-break/#possible-breaks
https://drafts.csswg.org/css-break/#forced-breaks

The essential change is that forced breaks are not allowed before a first child
or after a last child, only between siblings. Floats and auto-positioned
out-of-flow siblings after the last in-flow child still need to honor the
break-after value of said last in-flow child, though.

Updated the forced-break-before-complex-margin-collapsing.html test, since it
became invalid. Top margins after forced breaks should not be eaten by the
column boundary. It also made an incorrect assumption about inserting a forced
break in front of a a first child block. That's no valid class A break point.

BUG=223068,539873
==========

to

==========
Only allow forced fragmentainer breaks at class A break points.

https://drafts.csswg.org/css-break/#possible-breaks
https://drafts.csswg.org/css-break/#forced-breaks

The essential change is that forced breaks are not allowed before a first child
or after a last child, only between siblings. Floats and auto-positioned
out-of-flow siblings after the last in-flow child still need to honor the
break-after value of said last in-flow child, though.

Updated the forced-break-before-complex-margin-collapsing.html test, since it
became invalid. Top margins after forced breaks should not be eaten by the
column boundary. It also made an incorrect assumption about inserting a forced
break in front of a first child block. That's no valid class A break point.

This change also made printing/css2.1/page-break-after-003.html pass, which
has a break-after:page block with no in-flow block following it - i.e. there'll
be no class A break point for it to have any effect. It should not create a
blank page at the end.

BUG=223068,539873
==========

[mstensho (USE GERRIT), 2016-04-05 18:12:04]

mstensho@opera.com changed reviewers:
+ leviw@chromium.org

[mstensho (USE GERRIT), 2016-04-05 18:12:04]

I'm fairly confident that the bots have no reasons to cough at my patch now, so
then it's Levi's turn. :)

If you're interested in tests, but have a hard time choosing, the chef's
recommendation is LayoutTests/fragmentation/collapsing-class-a-breakpoints.html
- the others are mostly boring and straight-forward.

[leviw_travelin_and_unemployed, 2016-04-06 22:29:30]

FYI, I've begun reviewing this. It's taking me awhile to parse it all.

[mstensho (USE GERRIT), 2016-04-07 07:41:43]

On 2016/04/06 22:29:30, leviw wrote:
> FYI, I've begun reviewing this. It's taking me awhile to parse it all.

Great! Yeah, this is quite big, but it's the smallest patch I could think of,
without introducing intermediary regressions.

[leviw_travelin_and_unemployed, 2016-04-08 00:32:12]

Alright... LGTM. Thanks for the documentation that helped me get through this :)

[leviw_travelin_and_unemployed, 2016-04-08 00:32:15]

The CQ bit was checked by leviw@chromium.org

[commit-bot: I haz the power, 2016-04-08 00:32:47]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1856373002/40001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1856373002/40001

[commit-bot: I haz the power, 2016-04-08 03:00:45]

Description was changed from

==========
Only allow forced fragmentainer breaks at class A break points.

https://drafts.csswg.org/css-break/#possible-breaks
https://drafts.csswg.org/css-break/#forced-breaks

The essential change is that forced breaks are not allowed before a first child
or after a last child, only between siblings. Floats and auto-positioned
out-of-flow siblings after the last in-flow child still need to honor the
break-after value of said last in-flow child, though.

Updated the forced-break-before-complex-margin-collapsing.html test, since it
became invalid. Top margins after forced breaks should not be eaten by the
column boundary. It also made an incorrect assumption about inserting a forced
break in front of a first child block. That's no valid class A break point.

This change also made printing/css2.1/page-break-after-003.html pass, which
has a break-after:page block with no in-flow block following it - i.e. there'll
be no class A break point for it to have any effect. It should not create a
blank page at the end.

BUG=223068,539873
==========

to

==========
Only allow forced fragmentainer breaks at class A break points.

https://drafts.csswg.org/css-break/#possible-breaks
https://drafts.csswg.org/css-break/#forced-breaks

The essential change is that forced breaks are not allowed before a first child
or after a last child, only between siblings. Floats and auto-positioned
out-of-flow siblings after the last in-flow child still need to honor the
break-after value of said last in-flow child, though.

Updated the forced-break-before-complex-margin-collapsing.html test, since it
became invalid. Top margins after forced breaks should not be eaten by the
column boundary. It also made an incorrect assumption about inserting a forced
break in front of a first child block. That's no valid class A break point.

This change also made printing/css2.1/page-break-after-003.html pass, which
has a break-after:page block with no in-flow block following it - i.e. there'll
be no class A break point for it to have any effect. It should not create a
blank page at the end.

BUG=223068,539873
==========

[commit-bot: I haz the power, 2016-04-08 03:00:46]

Committed patchset #3 (id:40001)

[commit-bot: I haz the power, 2016-04-08 03:02:03]

Description was changed from

==========
Only allow forced fragmentainer breaks at class A break points.

https://drafts.csswg.org/css-break/#possible-breaks
https://drafts.csswg.org/css-break/#forced-breaks

The essential change is that forced breaks are not allowed before a first child
or after a last child, only between siblings. Floats and auto-positioned
out-of-flow siblings after the last in-flow child still need to honor the
break-after value of said last in-flow child, though.

Updated the forced-break-before-complex-margin-collapsing.html test, since it
became invalid. Top margins after forced breaks should not be eaten by the
column boundary. It also made an incorrect assumption about inserting a forced
break in front of a first child block. That's no valid class A break point.

This change also made printing/css2.1/page-break-after-003.html pass, which
has a break-after:page block with no in-flow block following it - i.e. there'll
be no class A break point for it to have any effect. It should not create a
blank page at the end.

BUG=223068,539873
==========

to

==========
Only allow forced fragmentainer breaks at class A break points.

https://drafts.csswg.org/css-break/#possible-breaks
https://drafts.csswg.org/css-break/#forced-breaks

The essential change is that forced breaks are not allowed before a first child
or after a last child, only between siblings. Floats and auto-positioned
out-of-flow siblings after the last in-flow child still need to honor the
break-after value of said last in-flow child, though.

Updated the forced-break-before-complex-margin-collapsing.html test, since it
became invalid. Top margins after forced breaks should not be eaten by the
column boundary. It also made an incorrect assumption about inserting a forced
break in front of a first child block. That's no valid class A break point.

This change also made printing/css2.1/page-break-after-003.html pass, which
has a break-after:page block with no in-flow block following it - i.e. there'll
be no class A break point for it to have any effect. It should not create a
blank page at the end.

BUG=223068,539873

Committed: https://crrev.com/893602648192952b73b33f060d7767c51b5440ed
Cr-Commit-Position: refs/heads/master@{#385955}
==========

[commit-bot: I haz the power, 2016-04-08 03:02:04]

Patchset 3 (id:??) landed as
https://crrev.com/893602648192952b73b33f060d7767c51b5440ed
Cr-Commit-Position: refs/heads/master@{#385955}