Initial support for nested multicol layout.

Initial support for nested multicol layout.

Nested column balancing doesn't work yet. Also no support for mapping visual
points to flow thread points (which is used by a few operations, but not by the
most common ones, like painting and hit-testing).

There are other corner-cases to sort out, too.

Still no support for printing multicol documents, but that's the ultimate goal
of this work.

BUG=447718
R=jchaffraix@chromium.org,leviw@chromium.org

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=200639

[leviw_travelin_and_unemployed, 2015-08-13 20:17:16]

I probably won't get to this until tomorrow, but looks exciting!

Is there by any chance an existing test suite that covers this work?

[mstensho (USE GERRIT), 2015-08-13 20:47:10]

On 2015/08/13 20:17:16, leviw wrote:
> I probably won't get to this until tomorrow, but looks exciting!
> 
> Is there by any chance an existing test suite that covers this work?

Not with -webkit- prefixes, for sure, but there's
https://github.com/w3c/csswg-test/tree/master/css-multicol-1

[leviw_travelin_and_unemployed, 2015-08-15 00:04:43]

LGTM.

Sorry, it took me awhile to wrap my head around all of this.

Do we have intentions of importing the w3c tests for this?

https://www.chromium.org/developers/design-documents/multi-column-layout could
probably also use an update.

https://codereview.chromium.org/1292163002/diff/1/Source/core/layout/LayoutMu...
File Source/core/layout/LayoutMultiColumnSet.cpp (right):

https://codereview.chromium.org/1292163002/diff/1/Source/core/layout/LayoutMu...
Source/core/layout/LayoutMultiColumnSet.cpp:121: { // extra scope here for
previousGroup; it's potentially invalid once we modify the m_fragmentainerGroups
Vector.
Nit: capitalize extra.

https://codereview.chromium.org/1292163002/diff/1/Source/core/layout/MultiCol...
File Source/core/layout/MultiColumnFragmentainerGroup.cpp (right):

https://codereview.chromium.org/1292163002/diff/1/Source/core/layout/MultiCol...
Source/core/layout/MultiColumnFragmentainerGroup.cpp:58:
ASSERT(m_maxColumnHeight != LayoutUnit::max());
Why this ASSERT? What situation are you testing for when this would occur?

[mstensho (USE GERRIT), 2015-08-17 07:43:09]

https://codereview.chromium.org/1292163002/diff/1/Source/core/layout/LayoutMu...
File Source/core/layout/LayoutMultiColumnSet.cpp (right):

https://codereview.chromium.org/1292163002/diff/1/Source/core/layout/LayoutMu...
Source/core/layout/LayoutMultiColumnSet.cpp:121: { // extra scope here for
previousGroup; it's potentially invalid once we modify the m_fragmentainerGroups
Vector.
On 2015/08/15 00:04:43, leviw wrote:
> Nit: capitalize extra.

done

https://codereview.chromium.org/1292163002/diff/1/Source/core/layout/MultiCol...
File Source/core/layout/MultiColumnFragmentainerGroup.cpp (right):

https://codereview.chromium.org/1292163002/diff/1/Source/core/layout/MultiCol...
Source/core/layout/MultiColumnFragmentainerGroup.cpp:58:
ASSERT(m_maxColumnHeight != LayoutUnit::max());
On 2015/08/15 00:04:43, leviw wrote:
> Why this ASSERT? What situation are you testing for when this would occur?

I wanted to make sure that calculateMaxColumnHeight() returns something
constrained. But we should be careful with treating LayoutUnit::max() as an
invalid value, since we may of course be dealing with an insanely tall outer
multicol container, in which case it will be LayoutUnit::max(). I'll just remove
this assertion.

[mstensho (USE GERRIT), 2015-08-17 07:44:18]

On 2015/08/15 00:04:43, leviw wrote:
> LGTM.
> 
> Sorry, it took me awhile to wrap my head around all of this.

More than fast enough. Thanks!

> Do we have intentions of importing the w3c tests for this?

I don't know. What's the general practice for things like this? Should I steal
(and adapt, i.e. prefix) some tests and create a fast/multicol/imported/ ?

> https://www.chromium.org/developers/design-documents/multi-column-layout could
> probably also use an update.

Absolutely. I'll write something there soon.

[mstensho (USE GERRIT), 2015-08-17 07:44:26]

The CQ bit was checked by mstensho@opera.com

[mstensho (USE GERRIT), 2015-08-17 07:44:26]

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/1292163002/#ps20001
(title: "code review")

[commit-bot: I haz the power, 2015-08-17 07:44:34]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1292163002/20001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1292163002/20001

[commit-bot: I haz the power, 2015-08-17 10:12:16]

Committed patchset #2 (id:20001) as
https://src.chromium.org/viewvc/blink?view=rev&revision=200639

[leviw_travelin_and_unemployed, 2015-08-17 20:00:17]

On 2015/08/17 at 07:44:18, mstensho wrote:
> On 2015/08/15 00:04:43, leviw wrote:
> > LGTM.
> > 
> > Sorry, it took me awhile to wrap my head around all of this.
> 
> More than fast enough. Thanks!
> 
> > Do we have intentions of importing the w3c tests for this?
> 
> I don't know. What's the general practice for things like this? Should I steal
(and adapt, i.e. prefix) some tests and create a fast/multicol/imported/ ?

I'm mostly just interested in the test coverage/compatibility. If you think
they're useful, you should go ahead and import them with prefixes. If you don't,
don't bother. Just curious if you were using it as a guide on what to fix.

> 
> > https://www.chromium.org/developers/design-documents/multi-column-layout
could
> > probably also use an update.
> 
> Absolutely. I'll write something there soon.

Awesome!