Refactor layoutBlock() and layoutBlockFlow(). Happens to fix bugs.

Refactor layoutBlock() and layoutBlockFlow(). Happens to fix bugs.

Move what only needs to be done once into layoutBlock(). Rename
layoutBlockFlow() to layoutChildren(). Establish LayoutState once, and compare
with the actual previous height to properly detect height changes.

This fixes two issues with the PaintLayerScrollableArea::FreezeScrollbarsScope
mechanism. Tests added.

1. We used to push LayoutState for the same object twice when freezing
scrollbars, which confused the fragmentation machinery.

2. We failed to detect height changes when freezing scrollbars, because we were
unable to compare against the original height (we compared against the height
we had when entering the second layout pass, rather than comparing against the
one we had when entering the first layout pass). We might therefore end up
skipping necessary re-layout of absolutely positioned descendants.

BUG=669039, 670660
Committed: https://crrev.com/9d96126f67850daf3c07586dc09fa334d592529c
Cr-Commit-Position: refs/heads/master@{#436414}

[mstensho (USE GERRIT), 2016-12-05 19:46:02]

The CQ bit was checked by mstensho@opera.com to run a CQ dry run

[commit-bot: I haz the power, 2016-12-05 19:46:29]

Dry run: CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[mstensho (USE GERRIT), 2016-12-05 19:46:57]

mstensho@opera.com changed reviewers:
+ szager@chromium.org

[szager1, 2016-12-05 21:17:31]

This is without question my favorite CL of 2016.

lgtm

[commit-bot: I haz the power, 2016-12-05 21:22:35]

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

[commit-bot: I haz the power, 2016-12-05 21:22:36]

Dry run: This issue passed the CQ dry run.

[mstensho (USE GERRIT), 2016-12-05 21:25:23]

The CQ bit was checked by mstensho@opera.com

[commit-bot: I haz the power, 2016-12-05 21:26:06]

CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2016-12-05 21:31:11]

CQ is committing da patch.

Bot data: {"patchset_id": 1, "attempt_start_ts": 1480973123405410, "parent_rev":
"88c799569c1ab1b07014f910edfc15dc666880de", "commit_rev":
"b04cb25eeae02711c46bf847f9f2037de948d4a7"}

[commit-bot: I haz the power, 2016-12-05 21:31:38]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2016-12-05 21:35:13]

Description was changed from

==========
Refactor layoutBlock() and layoutBlockFlow(). Happens to fix bugs.

Move what only needs to be done once into layoutBlock(). Rename
layoutBlockFlow() to layoutChildren(). Establish LayoutState once, and compare
with the actual previous height to properly detect height changes.

This fixes two issues with the PaintLayerScrollableArea::FreezeScrollbarsScope
mechanism. Tests added.

1. We used to push LayoutState for the same object twice when freezing
scrollbars, which confused the fragmentation machinery.

2. We failed to detect height changes when freezing scrollbars, because we were
unable to compare against the original height (we compared against the height
we had when entering the second layout pass, rather than comparing against the
one we had when entering the first layout pass). We might therefore end up
skipping necessary re-layout of absolutely positioned descendants.

BUG=669039,670660
==========

to

==========
Refactor layoutBlock() and layoutBlockFlow(). Happens to fix bugs.

Move what only needs to be done once into layoutBlock(). Rename
layoutBlockFlow() to layoutChildren(). Establish LayoutState once, and compare
with the actual previous height to properly detect height changes.

This fixes two issues with the PaintLayerScrollableArea::FreezeScrollbarsScope
mechanism. Tests added.

1. We used to push LayoutState for the same object twice when freezing
scrollbars, which confused the fragmentation machinery.

2. We failed to detect height changes when freezing scrollbars, because we were
unable to compare against the original height (we compared against the height
we had when entering the second layout pass, rather than comparing against the
one we had when entering the first layout pass). We might therefore end up
skipping necessary re-layout of absolutely positioned descendants.

BUG=669039,670660

Committed: https://crrev.com/9d96126f67850daf3c07586dc09fa334d592529c
Cr-Commit-Position: refs/heads/master@{#436414}
==========

[commit-bot: I haz the power, 2016-12-05 21:35:14]

Patchset 1 (id:??) landed as
https://crrev.com/9d96126f67850daf3c07586dc09fa334d592529c
Cr-Commit-Position: refs/heads/master@{#436414}