Keep block pagination struts after layout, and store them before any type of break.

Keep block pagination struts after layout, and store them before any type of break.

Any block-level object (block container, block-displayed image, for instance)
may now have a strut, so this is stored in the rare data section of LayoutBox.

Added layout tests for things that I nearly broke or wanted to make sure that I
didn't break, while working on this.

No behavioral changes are intended with this CL, and because struts aren't
web-exposed, I added a few "unit tests" for pagination struts.

This is a preparatory patch for refactoring the column balancing
implementation to do everything after layout, instead of during layout (will
fix bugs, get rid of the rather esoteric setPageBreak() calls scattered around,
and also make it easier to do optimizations in the future, instead of doing
almost unconditional deep layout passes when doing multicol or printing).

R=jchaffraix@chromium.org,leviw@chromium.org

Committed: https://crrev.com/d956b23cdf5ea03eb1cf350cb5ca827745b8310a
Cr-Commit-Position: refs/heads/master@{#352804}

[leviw_travelin_and_unemployed, 2015-10-06 13:17:59]

https://codereview.chromium.org/1375673004/diff/1/third_party/WebKit/Source/c...
File third_party/WebKit/Source/core/layout/LayoutBlockFlow.cpp (right):

https://codereview.chromium.org/1375673004/diff/1/third_party/WebKit/Source/c...
third_party/WebKit/Source/core/layout/LayoutBlockFlow.cpp:698:
child.setPaginationStrut(LayoutUnit());
We should probably have a resetPaginationStrut() method :)

https://codereview.chromium.org/1375673004/diff/1/third_party/WebKit/Source/c...
third_party/WebKit/Source/core/layout/LayoutBlockFlow.cpp:701: // only block
flows support strut propagation, but this may (and should) change in the future.
Seems bug-worthy for more context.

https://codereview.chromium.org/1375673004/diff/1/third_party/WebKit/Source/c...
third_party/WebKit/Source/core/layout/LayoutBlockFlow.cpp:2437: if
(strutFromUnsplittable)
You switched the order of this logic from the old version. Why? The old version
would only call adjustForUnsplittableChild in the else clause, which should be
cheaper, no? That method seems expensive.

[mstensho (USE GERRIT), 2015-10-06 14:01:45]

https://codereview.chromium.org/1375673004/diff/1/third_party/WebKit/Source/c...
File third_party/WebKit/Source/core/layout/LayoutBlockFlow.cpp (right):

https://codereview.chromium.org/1375673004/diff/1/third_party/WebKit/Source/c...
third_party/WebKit/Source/core/layout/LayoutBlockFlow.cpp:698:
child.setPaginationStrut(LayoutUnit());
On 2015/10/06 13:17:59, leviw wrote:
> We should probably have a resetPaginationStrut() method :)

Done.

https://codereview.chromium.org/1375673004/diff/1/third_party/WebKit/Source/c...
third_party/WebKit/Source/core/layout/LayoutBlockFlow.cpp:701: // only block
flows support strut propagation, but this may (and should) change in the future.
On 2015/10/06 13:17:59, leviw wrote:
> Seems bug-worthy for more context.

Done.

https://codereview.chromium.org/1375673004/diff/1/third_party/WebKit/Source/c...
third_party/WebKit/Source/core/layout/LayoutBlockFlow.cpp:2437: if
(strutFromUnsplittable)
On 2015/10/06 13:17:59, leviw wrote:
> You switched the order of this logic from the old version. Why? The old
version
> would only call adjustForUnsplittableChild in the else clause, which should be
> cheaper, no? That method seems expensive.

Seems that I had no good reason for making this change. Switching back.

[leviw_travelin_and_unemployed, 2015-10-07 07:38:21]

lgtm

[mstensho (USE GERRIT), 2015-10-07 07:38:35]

The CQ bit was checked by mstensho@opera.com

[commit-bot: I haz the power, 2015-10-07 07:40:52]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1375673004/20001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1375673004/20001

[commit-bot: I haz the power, 2015-10-07 08:54:04]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-10-07 08:55:11]

Patchset 2 (id:??) landed as
https://crrev.com/d956b23cdf5ea03eb1cf350cb5ca827745b8310a
Cr-Commit-Position: refs/heads/master@{#352804}