Deduct pagination struts when calculating initial column height.

Deduct pagination struts when calculating initial column height.

Even if height is auto, nested multicol sets a column height in the initial
layout pass (set to the remaining height in the outer multicol container; this
all takes place in resetColumnHeight()), which enables pagination in the first
layout pass, and may thus insert pagination struts. We need to exclude those
when calculating the initial balanced column height estimate. The reason why we
set this height before layout in this case, is that we need to figure out how
many fragmentainer groups (rows) we need.

In the future, we may also consider setting a height before layout for
non-nested auto-height multicol containers, as an optimiation, since that may
reduce the number of layout passes in some cases.

Cleaned up the code in MultiColumnFragmentainerGroup::resetColumnHeight(). No
behavioral changes there, and the TODO is adressed with this CL.

R=leviw@chromium.org
BUG=447718
Committed: https://crrev.com/2a88bf4073c19256c607f2224b013156b50f7430
Cr-Commit-Position: refs/heads/master@{#357338}

[mstensho (USE GERRIT), 2015-10-30 14:13:31]

Levi: there are are more goodies (albeit somewhat less beefy) waiting, once this
one lands. :)

[leviw_travelin_and_unemployed, 2015-10-30 20:10:50]

Sorry, I had some comments I forgot to hit "send" on! Thanks for the ping.

Changes LGTM. Just a couple comments.

https://codereview.chromium.org/1420713003/diff/1/third_party/WebKit/Source/c...
File third_party/WebKit/Source/core/layout/ColumnBalancer.cpp (right):

https://codereview.chromium.org/1420713003/diff/1/third_party/WebKit/Source/c...
third_party/WebKit/Source/core/layout/ColumnBalancer.cpp:142: LayoutUnit
totalStrut;
totalStrutSpace or something like that?

https://codereview.chromium.org/1420713003/diff/1/third_party/WebKit/Source/c...
File third_party/WebKit/Source/core/layout/ColumnBalancer.h (right):

https://codereview.chromium.org/1420713003/diff/1/third_party/WebKit/Source/c...
third_party/WebKit/Source/core/layout/ColumnBalancer.h:39: // Examine and
collect column balancing data from a line that has been found to intersect with
Maybe also mention here that we record strut information as well?

https://codereview.chromium.org/1420713003/diff/1/third_party/WebKit/Source/c...
third_party/WebKit/Source/core/layout/ColumnBalancer.h:140: Vector<LayoutUnit,
32> m_struts;
m_shortestStruts maybe? (I do love the comment, though!)

[mstensho (USE GERRIT), 2015-11-02 09:12:28]

https://codereview.chromium.org/1420713003/diff/1/third_party/WebKit/Source/c...
File third_party/WebKit/Source/core/layout/ColumnBalancer.cpp (right):

https://codereview.chromium.org/1420713003/diff/1/third_party/WebKit/Source/c...
third_party/WebKit/Source/core/layout/ColumnBalancer.cpp:142: LayoutUnit
totalStrut;
On 2015/10/30 20:10:50, leviw wrote:
> totalStrutSpace or something like that?

Done.

https://codereview.chromium.org/1420713003/diff/1/third_party/WebKit/Source/c...
File third_party/WebKit/Source/core/layout/ColumnBalancer.h (right):

https://codereview.chromium.org/1420713003/diff/1/third_party/WebKit/Source/c...
third_party/WebKit/Source/core/layout/ColumnBalancer.h:39: // Examine and
collect column balancing data from a line that has been found to intersect with
On 2015/10/30 20:10:50, leviw wrote:
> Maybe also mention here that we record strut information as well?

I decided against that. That's just mighty fine column balancing data, if you
ask me. :)

This is a pure virtual method, and I'd rather try to be generic and not list
everything that overrides might end up doing.

https://codereview.chromium.org/1420713003/diff/1/third_party/WebKit/Source/c...
third_party/WebKit/Source/core/layout/ColumnBalancer.h:140: Vector<LayoutUnit,
32> m_struts;
On 2015/10/30 20:10:50, leviw wrote:
> m_shortestStruts maybe? (I do love the comment, though!)

Done.

[mstensho (USE GERRIT), 2015-11-02 09:12:47]

The CQ bit was checked by mstensho@opera.com

[mstensho (USE GERRIT), 2015-11-02 09:12:47]

The patchset sent to the CQ was uploaded after l-g-t-m from leviw@chromium.org
Link to the patchset: https://codereview.chromium.org/1420713003/#ps20001
(title: "Code review")

[commit-bot: I haz the power, 2015-11-02 09:13:09]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1420713003/20001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1420713003/20001

[commit-bot: I haz the power, 2015-11-02 12:05:35]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-11-02 12:06:26]

Patchset 2 (id:??) landed as
https://crrev.com/2a88bf4073c19256c607f2224b013156b50f7430
Cr-Commit-Position: refs/heads/master@{#357338}