[New Multicolumn] Support for block direction margins on spanners.

[New Multicolumn] Support for block direction margins on spanners.

Block direction margins need to be copied from the column-span:all element
to its placeholder, since it's the placeholder that gets laid out and
positioned among other placeholders and column sets within the multicol
container.

Also prevent margin-collapsing through column sets, since that suddenly
matters.

Note that inline direction margins were already working. Some of the
tests in this CL also test those.

BUG=347325
R=jchaffraix@chromium.org

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=188696

[Julien - ping for review, 2015-01-20 08:55:15]

https://codereview.chromium.org/855413002/diff/1/LayoutTests/fast/multicol/sp...
File LayoutTests/fast/multicol/span/change-spanner-margins.html (right):

https://codereview.chromium.org/855413002/diff/1/LayoutTests/fast/multicol/sp...
LayoutTests/fast/multicol/span/change-spanner-margins.html:2: <p>Below there
should be a blue square with a thick black border.</p>
and no visible FAIL?

https://codereview.chromium.org/855413002/diff/1/LayoutTests/fast/multicol/sp...
File LayoutTests/fast/multicol/span/simple-margins.html (right):

https://codereview.chromium.org/855413002/diff/1/LayoutTests/fast/multicol/sp...
LayoutTests/fast/multicol/span/simple-margins.html:2: <p>Below there should be
yellow square centered inside a blue square.</p>
and no red?

https://codereview.chromium.org/855413002/diff/1/Source/core/rendering/Render...
File Source/core/rendering/RenderMultiColumnSpannerPlaceholder.cpp (right):

https://codereview.chromium.org/855413002/diff/1/Source/core/rendering/Render...
Source/core/rendering/RenderMultiColumnSpannerPlaceholder.cpp:50:
setStyle(newStyle);
Won't this trigger another run through styleWillChange / styleDidChange?

[mstensho (USE GERRIT), 2015-01-20 09:23:30]

https://codereview.chromium.org/855413002/diff/1/LayoutTests/fast/multicol/sp...
File LayoutTests/fast/multicol/span/change-spanner-margins.html (right):

https://codereview.chromium.org/855413002/diff/1/LayoutTests/fast/multicol/sp...
LayoutTests/fast/multicol/span/change-spanner-margins.html:2: <p>Below there
should be a blue square with a thick black border.</p>
On 2015/01/20 08:55:14, Julien Chaffraix - CET wrote:
> and no visible FAIL?

Done.

https://codereview.chromium.org/855413002/diff/1/LayoutTests/fast/multicol/sp...
File LayoutTests/fast/multicol/span/simple-margins.html (right):

https://codereview.chromium.org/855413002/diff/1/LayoutTests/fast/multicol/sp...
LayoutTests/fast/multicol/span/simple-margins.html:2: <p>Below there should be
yellow square centered inside a blue square.</p>
On 2015/01/20 08:55:15, Julien Chaffraix - CET wrote:
> and no red?

Done.

https://codereview.chromium.org/855413002/diff/1/Source/core/rendering/Render...
File Source/core/rendering/RenderMultiColumnSpannerPlaceholder.cpp (right):

https://codereview.chromium.org/855413002/diff/1/Source/core/rendering/Render...
Source/core/rendering/RenderMultiColumnSpannerPlaceholder.cpp:50:
setStyle(newStyle);
On 2015/01/20 08:55:15, Julien Chaffraix - CET wrote:
> Won't this trigger another run through styleWillChange / styleDidChange?

Yeah, but on this object, not on the RenderBox that has column-span:all.

[Julien - ping for review, 2015-01-20 16:52:46]

lgtm

https://codereview.chromium.org/855413002/diff/1/Source/core/rendering/Render...
File Source/core/rendering/RenderMultiColumnSpannerPlaceholder.cpp (right):

https://codereview.chromium.org/855413002/diff/1/Source/core/rendering/Render...
Source/core/rendering/RenderMultiColumnSpannerPlaceholder.cpp:50:
setStyle(newStyle);
On 2015/01/20 09:23:30, mstensho wrote:
> On 2015/01/20 08:55:15, Julien Chaffraix - CET wrote:
> > Won't this trigger another run through styleWillChange / styleDidChange?
> 
> Yeah, but on this object, not on the RenderBox that has column-span:all.

Morten made me realize on IRC that we can't skip the setStyle. This is how the
style is propagated to anonymous renderers and it's the only safe way to do it.

https://codereview.chromium.org/855413002/diff/20001/LayoutTests/fast/multico...
File LayoutTests/fast/multicol/span/adjacent-spanners-with-margin.html (right):

https://codereview.chromium.org/855413002/diff/20001/LayoutTests/fast/multico...
LayoutTests/fast/multicol/span/adjacent-spanners-with-margin.html:2: <p>There
should be a blue square below.</p>
Let's add a description to the tests about what is tested.

[mstensho (USE GERRIT), 2015-01-20 17:09:22]

https://codereview.chromium.org/855413002/diff/20001/LayoutTests/fast/multico...
File LayoutTests/fast/multicol/span/adjacent-spanners-with-margin.html (right):

https://codereview.chromium.org/855413002/diff/20001/LayoutTests/fast/multico...
LayoutTests/fast/multicol/span/adjacent-spanners-with-margin.html:2: <p>There
should be a blue square below.</p>
On 2015/01/20 16:52:46, Julien Chaffraix - CET wrote:
> Let's add a description to the tests about what is tested.

Done.

[mstensho (USE GERRIT), 2015-01-20 17:09:50]

The CQ bit was checked by mstensho@opera.com

[commit-bot: I haz the power, 2015-01-20 17:10:38]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/855413002/40001

[commit-bot: I haz the power, 2015-01-20 18:44:30]

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

[commit-bot: I haz the power, 2015-01-20 18:44:31]

Try jobs failed on following builders:
  win_blink_rel on tryserver.blink
(http://build.chromium.org/p/tryserver.blink/builders/win_blink_rel/builds/46980)

[mstensho (USE GERRIT), 2015-01-20 19:25:10]

The CQ bit was checked by mstensho@opera.com

[commit-bot: I haz the power, 2015-01-20 19:26:05]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/855413002/40001

[commit-bot: I haz the power, 2015-01-20 21:11:36]

Committed patchset #3 (id:40001) as
https://src.chromium.org/viewvc/blink?view=rev&revision=188696