Simplify MultiColumnFragmentainerGroup::collectLayerFragments().

Simplify MultiColumnFragmentainerGroup::collectLayerFragments().

No need to do so much stuff on our own in there, when we already have methods
that can do it for us.

This is just clean-up; no behavioral changes intended.

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

Committed: https://crrev.com/1295b7ec94e0e05cd85c7e96862939d61093523f
git-svn-id: svn://svn.chromium.org/blink/trunk@199595 bbb929c8-8fbe-4397-9dbb-9b2b20218538

[leviw_travelin_and_unemployed, 2015-07-28 18:48:37]

The CQ bit was checked by leviw@chromium.org

[leviw_travelin_and_unemployed, 2015-07-28 18:48:38]

lgtm

https://codereview.chromium.org/1252863005/diff/1/Source/core/layout/MultiCol...
File Source/core/layout/MultiColumnFragmentainerGroup.cpp (left):

https://codereview.chromium.org/1252863005/diff/1/Source/core/layout/MultiCol...
Source/core/layout/MultiColumnFragmentainerGroup.cpp:243: // Get the portion of
the flow thread that corresponds to this column.
Wow. That's a lot of code to remove.

https://codereview.chromium.org/1252863005/diff/1/Source/core/layout/MultiCol...
File Source/core/layout/MultiColumnFragmentainerGroup.cpp (right):

https://codereview.chromium.org/1252863005/diff/1/Source/core/layout/MultiCol...
Source/core/layout/MultiColumnFragmentainerGroup.cpp:442: LayoutRect
MultiColumnFragmentainerGroup::flowThreadPortionOverflowRectAt(unsigned
columnIndex) const
That's way nicer :)

[commit-bot: I haz the power, 2015-07-28 18:48:50]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1252863005/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1252863005/1

[commit-bot: I haz the power, 2015-07-28 18:51:34]

Committed patchset #1 (id:1) as
https://src.chromium.org/viewvc/blink?view=rev&revision=199595

[commit-bot: I haz the power, 2015-09-23 11:51:18]

Patchset 1 (id:??) landed as
https://crrev.com/1295b7ec94e0e05cd85c7e96862939d61093523f