Ability to return the height of fragmentainer groups that don't yet exist.

Ability to return the height of fragmentainer groups that don't yet exist.

When the flow thread offset is out of range (i.e. it comes after the logical
bottom of the last fragmentainer group created so far) when asking for a column
height, estimate how tall the next fragmentainer group will be, instead of
returning the height of the last fragmentainer group.

It was dodgy of LayoutBlockFlow::adjustLinePositionForPagination() to call
paginatedContentWasLaidOut() before the final position of the line had been
determined, but we did so in order to create the necessary fragmentainer
groups, so that we could get the right column height. However, since we may
decide to drop the strut calculated if a line is taller than the column, we'd
better not pretend that we applied the strut. Otherwise we may create more
fragmentainer groups than necessary, causing mild confusion and assertion
failures in the multicol machinery.

To fix this, we need LayoutBlock::pageLogicalHeightForOffset() to be able to
return the height of columns in a fragmentainer group that has't yet been
created (and perhaps never will). The rationale behind this solution is that it
seems better to deal with this inside the multicol implementation, than to add
more complexity in adjustLinePositionForPagination(). Leaving LayoutBlockFlow
blissfully unaware of multiple fragmentainer groups seems like a good thing.

BUG=552615
Committed: https://crrev.com/3f96177578cf0511174d42546a70660cc8d6eeeb
Cr-Commit-Position: refs/heads/master@{#377256}

[mstensho (USE GERRIT), 2016-02-22 19:36:45]

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

[leviw_travelin_and_unemployed, 2016-02-23 18:56:17]

This is messy, but so was the other 'solution' :) LGTM.

https://codereview.chromium.org/1710843003/diff/1/third_party/WebKit/Source/c...
File third_party/WebKit/Source/core/layout/LayoutMultiColumnSet.cpp (right):

https://codereview.chromium.org/1710843003/diff/1/third_party/WebKit/Source/c...
third_party/WebKit/Source/core/layout/LayoutMultiColumnSet.cpp:90: // space of
the enclosing fragmentation context here, but that's hard, since the offset
Ugh.

[mstensho (USE GERRIT), 2016-02-23 19:00:48]

On 2016/02/23 18:56:17, leviw wrote:
> This is messy, but so was the other 'solution' :) LGTM.

Messy indeed. It's the best I've been able to come up with so far. Thanks for
reviewing. Now go wash your eyes. :)

[mstensho (USE GERRIT), 2016-02-23 19:00:54]

The CQ bit was checked by mstensho@opera.com

[commit-bot: I haz the power, 2016-02-23 19:06:46]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1710843003/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1710843003/1

[commit-bot: I haz the power, 2016-02-23 22:16:49]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2016-02-23 22:16:50]

Try jobs failed on following builders:
  win_chromium_rel_ng on tryserver.chromium.win (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.win/builders/win_chromium_rel_...)

[mstensho (USE GERRIT), 2016-02-24 09:05:26]

The CQ bit was checked by mstensho@opera.com

[commit-bot: I haz the power, 2016-02-24 09:06:42]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1710843003/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1710843003/1

[commit-bot: I haz the power, 2016-02-24 10:08:26]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2016-02-24 10:09:32]

Description was changed from

==========
Ability to return the height of fragmentainer groups that don't yet exist.

When the flow thread offset is out of range (i.e. it comes after the logical
bottom of the last fragmentainer group created so far) when asking for a column
height, estimate how tall the next fragmentainer group will be, instead of
returning the height of the last fragmentainer group.

It was dodgy of LayoutBlockFlow::adjustLinePositionForPagination() to call
paginatedContentWasLaidOut() before the final position of the line had been
determined, but we did so in order to create the necessary fragmentainer
groups, so that we could get the right column height. However, since we may
decide to drop the strut calculated if a line is taller than the column, we'd
better not pretend that we applied the strut. Otherwise we may create more
fragmentainer groups than necessary, causing mild confusion and assertion
failures in the multicol machinery.

To fix this, we need LayoutBlock::pageLogicalHeightForOffset() to be able to
return the height of columns in a fragmentainer group that has't yet been
created (and perhaps never will). The rationale behind this solution is that it
seems better to deal with this inside the multicol implementation, than to add
more complexity in adjustLinePositionForPagination(). Leaving LayoutBlockFlow
blissfully unaware of multiple fragmentainer groups seems like a good thing.

BUG=552615
==========

to

==========
Ability to return the height of fragmentainer groups that don't yet exist.

When the flow thread offset is out of range (i.e. it comes after the logical
bottom of the last fragmentainer group created so far) when asking for a column
height, estimate how tall the next fragmentainer group will be, instead of
returning the height of the last fragmentainer group.

It was dodgy of LayoutBlockFlow::adjustLinePositionForPagination() to call
paginatedContentWasLaidOut() before the final position of the line had been
determined, but we did so in order to create the necessary fragmentainer
groups, so that we could get the right column height. However, since we may
decide to drop the strut calculated if a line is taller than the column, we'd
better not pretend that we applied the strut. Otherwise we may create more
fragmentainer groups than necessary, causing mild confusion and assertion
failures in the multicol machinery.

To fix this, we need LayoutBlock::pageLogicalHeightForOffset() to be able to
return the height of columns in a fragmentainer group that has't yet been
created (and perhaps never will). The rationale behind this solution is that it
seems better to deal with this inside the multicol implementation, than to add
more complexity in adjustLinePositionForPagination(). Leaving LayoutBlockFlow
blissfully unaware of multiple fragmentainer groups seems like a good thing.

BUG=552615

Committed: https://crrev.com/3f96177578cf0511174d42546a70660cc8d6eeeb
Cr-Commit-Position: refs/heads/master@{#377256}
==========

[commit-bot: I haz the power, 2016-02-24 10:09:33]

Patchset 1 (id:??) landed as
https://crrev.com/3f96177578cf0511174d42546a70660cc8d6eeeb
Cr-Commit-Position: refs/heads/master@{#377256}