Make LayoutFlowThread::fragmentsBoundingBox() faster.

Make LayoutFlowThread::fragmentsBoundingBox() faster.

It used to let collectLayerFragments() handle the job, with an infinite dirty
rectangle. This forced us to collect all columns, when we really only needed to
know the bounding boxes of the first and the last columns in each fragmentainer
group.

This gives a major speed-up in the Layout/multicol/tall-content-short-columns-*
tests. It will also make it possible to submit a fix for bug 502407 and write a
test for it that doesn't time out.

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

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=200264

[leviw_travelin_and_unemployed, 2015-08-03 21:33:00]

LGTM, but if Julien can give it a second set of eyes I'll feel better.

https://codereview.chromium.org/1265933002/diff/1/Source/core/layout/MultiCol...
File Source/core/layout/MultiColumnFragmentainerGroup.cpp (right):

https://codereview.chromium.org/1265933002/diff/1/Source/core/layout/MultiCol...
Source/core/layout/MultiColumnFragmentainerGroup.cpp:178: LayoutRect
MultiColumnFragmentainerGroup::fragmentsBoundingBox(const LayoutRect&
boundingBoxInFlowThread) const
It's difficult for me to be 100% certain of this code, but it seems right.

https://codereview.chromium.org/1265933002/diff/1/Source/core/layout/MultiCol...
Source/core/layout/MultiColumnFragmentainerGroup.cpp:186: LayoutUnit
boundingBoxLogicalBottom = (isHorizontalWritingMode ?
flippedBoundingBoxInFlowThread.maxY() : flippedBoundingBoxInFlowThread.maxX());
Nit: inconsistent parenthesis usage. Perhaps you should just put both of these
in an if/else.

[mstensho (USE GERRIT), 2015-08-04 10:48:11]

Julien, wdyt?

https://codereview.chromium.org/1265933002/diff/1/Source/core/layout/MultiCol...
File Source/core/layout/MultiColumnFragmentainerGroup.cpp (right):

https://codereview.chromium.org/1265933002/diff/1/Source/core/layout/MultiCol...
Source/core/layout/MultiColumnFragmentainerGroup.cpp:186: LayoutUnit
boundingBoxLogicalBottom = (isHorizontalWritingMode ?
flippedBoundingBoxInFlowThread.maxY() : flippedBoundingBoxInFlowThread.maxX());
On 2015/08/03 21:33:00, leviw wrote:
> Nit: inconsistent parenthesis usage. Perhaps you should just put both of these
> in an if/else.

No idea where those extraneous parentheses came from (I normally try to use as
few as the compiler settings allow). I just removed them.

Done.

[mstensho (USE GERRIT), 2015-08-06 11:18:27]

@jchaffraix, leviw needs your help to feel better. :)

[mstensho (USE GERRIT), 2015-08-10 12:17:41]

ping jchaffraix

[leviw_travelin_and_unemployed, 2015-08-10 19:38:45]

I gave this some more thought and I'd rather not hold it up. Hitting the CQ.

[leviw_travelin_and_unemployed, 2015-08-10 19:38:48]

The CQ bit was checked by leviw@chromium.org

[leviw_travelin_and_unemployed, 2015-08-10 19:38:48]

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/1265933002/#ps20001
(title: "Code review.")

[commit-bot: I haz the power, 2015-08-10 19:38:54]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1265933002/20001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1265933002/20001

[commit-bot: I haz the power, 2015-08-10 21:06:08]

Committed patchset #2 (id:20001) as
https://src.chromium.org/viewvc/blink?view=rev&revision=200264

[esprehn, 2015-08-13 18:29:58]

Amazing! Next time you should add BUG=502407 so this gets posted there too. :)