Allow flow thread portion logical bottom to be above its logical top.

Allow flow thread portion logical bottom to be above its logical top.

We used to try to prevent this, as an attempt to make sure that no
fragmentainer group would have overlapping flow thread portion rectangles with
other fragmentainer groups. But that was already easily achievable with e.g. an
empty block between two column spanners anyway.

There is a legitimate reason for the flow thread portion bottom to be above the
top: negative margins.

Introduce MultiColumnFragmentainerGroup::logicalHeightInFlowThreadAt().
Less duplicated code. Some extra care is now needed, to make sure that we don't
end up with negative logical heights.

BUG=688760, 683090, 683554
Review-Url: https://codereview.chromium.org/2709013007
Cr-Commit-Position: refs/heads/master@{#453201}
Committed: https://chromium.googlesource.com/chromium/src/+/0b389da84405eef38ee9f9e54f51352a6c1508f3

[mstensho (USE GERRIT), 2017-02-23 19:37:28]

The CQ bit was checked by mstensho@opera.com to run a CQ dry run

[commit-bot: I haz the power, 2017-02-23 19:37:57]

Dry run: CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2017-02-23 21:08:40]

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

[commit-bot: I haz the power, 2017-02-23 21:08:41]

Dry run: This issue passed the CQ dry run.

[mstensho (USE GERRIT), 2017-02-23 22:01:22]

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

[eae, 2017-02-23 22:20:20]

LGTM w/suggestions

https://codereview.chromium.org/2709013007/diff/1/third_party/WebKit/Source/c...
File third_party/WebKit/Source/core/layout/LayoutMultiColumnSet.h (right):

https://codereview.chromium.org/2709013007/diff/1/third_party/WebKit/Source/c...
third_party/WebKit/Source/core/layout/LayoutMultiColumnSet.h:151: LayoutUnit
logicalHeightInFlowThread() const {
Would you mind adding a comment here explaining how this could be negative (i.e.
if the top is above the bottom). For most casual readers that would seem to be
impossible thus making this check seem unnecessary.

[mstensho (USE GERRIT), 2017-02-27 11:57:05]

https://codereview.chromium.org/2709013007/diff/1/third_party/WebKit/Source/c...
File third_party/WebKit/Source/core/layout/LayoutMultiColumnSet.h (right):

https://codereview.chromium.org/2709013007/diff/1/third_party/WebKit/Source/c...
third_party/WebKit/Source/core/layout/LayoutMultiColumnSet.h:151: LayoutUnit
logicalHeightInFlowThread() const {
On 2017/02/23 22:20:20, eae wrote:
> Would you mind adding a comment here explaining how this could be negative
(i.e.
> if the top is above the bottom). For most casual readers that would seem to be
> impossible thus making this check seem unnecessary. 

Good idea. Done.

[mstensho (USE GERRIT), 2017-02-27 11:57:10]

The CQ bit was checked by mstensho@opera.com

[mstensho (USE GERRIT), 2017-02-27 11:57:10]

The patchset sent to the CQ was uploaded after l-g-t-m from eae@chromium.org
Link to the patchset: https://codereview.chromium.org/2709013007/#ps20001
(title: "Add clarifying comment in logicalHeightInFlowThread()")

[commit-bot: I haz the power, 2017-02-27 11:57:24]

CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2017-02-27 13:47:06]

CQ is committing da patch.

Bot data: {"patchset_id": 20001, "attempt_start_ts": 1488196630037810,
"parent_rev": "60c2e708f18b501cfbea9a3d9a5a8ef8a5a3d9e4", "commit_rev":
"0b389da84405eef38ee9f9e54f51352a6c1508f3"}

[commit-bot: I haz the power, 2017-02-27 13:47:45]

Description was changed from

==========
Allow flow thread portion logical bottom to be above its logical top.

We used to try to prevent this, as an attempt to make sure that no
fragmentainer group would have overlapping flow thread portion rectangles with
other fragmentainer groups. But that was already easily achievable with e.g. an
empty block between two column spanners anyway.

There is a legitimate reason for the flow thread portion bottom to be above the
top: negative margins.

Introduce MultiColumnFragmentainerGroup::logicalHeightInFlowThreadAt().
Less duplicated code. Some extra care is now needed, to make sure that we don't
end up with negative logical heights.

BUG=688760,683090,683554
==========

to

==========
Allow flow thread portion logical bottom to be above its logical top.

We used to try to prevent this, as an attempt to make sure that no
fragmentainer group would have overlapping flow thread portion rectangles with
other fragmentainer groups. But that was already easily achievable with e.g. an
empty block between two column spanners anyway.

There is a legitimate reason for the flow thread portion bottom to be above the
top: negative margins.

Introduce MultiColumnFragmentainerGroup::logicalHeightInFlowThreadAt().
Less duplicated code. Some extra care is now needed, to make sure that we don't
end up with negative logical heights.

BUG=688760,683090,683554

Review-Url: https://codereview.chromium.org/2709013007
Cr-Commit-Position: refs/heads/master@{#453201}
Committed:
https://chromium.googlesource.com/chromium/src/+/0b389da84405eef38ee9f9e54f51...
==========

[commit-bot: I haz the power, 2017-02-27 13:47:46]

Committed patchset #2 (id:20001) as
https://chromium.googlesource.com/chromium/src/+/0b389da84405eef38ee9f9e54f51...