Move self-collapse checking to LayoutBlockFlow and cache it completely.

Move self-collapse checking to LayoutBlockFlow and cache it completely.

Only block containers (that's LayoutBlockFlow in Blinquese) can have adjoining
top and bottom margins, since all other LayoutBlock derivates establish some
kind of formatting context (table, flexbox, etc.).

Also cache self-collapsedness completely. Previously we only used the cached
result if we had previously found that the entire subtree is self-collapsing.
The new approach eliminates the need for "mutable" too.

BUG=302024
Committed: https://crrev.com/43862543cb7622a39c6fbc7895ffe03ba5337f54
Cr-Commit-Position: refs/heads/master@{#390729}

[mstensho (USE GERRIT), 2016-04-29 18:23:06]

mstensho@opera.com changed reviewers:
+ eae@chromium.org, leviw@chromium.org, szager@chromium.org,
wkorman@chromium.org

[leviw_travelin_and_unemployed, 2016-04-29 20:06:28]

The CQ bit was checked by leviw@chromium.org

[leviw_travelin_and_unemployed, 2016-04-29 20:06:29]

lgtm

Awesome!

[commit-bot: I haz the power, 2016-04-29 20:07:10]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1933153002/20001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1933153002/20001

[commit-bot: I haz the power, 2016-04-29 20:12:08]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2016-04-30 17:28:08]

Patchset 2 (id:??) landed as
https://crrev.com/43862543cb7622a39c6fbc7895ffe03ba5337f54
Cr-Commit-Position: refs/heads/master@{#390729}

[commit-bot: I haz the power, 2016-04-30 18:02:00]

Description was changed from

==========
Move self-collapse checking to LayoutBlockFlow and cache it completely.

Only block containers (that's LayoutBlockFlow in Blinquese) can have adjoining
top and bottom margins, since all other LayoutBlock derivates establish some
kind of formatting context (table, flexbox, etc.).

Also cache self-collapsedness completely. Previously we only used the cached
result if we had previously found that the entire subtree is self-collapsing.
The new approach eliminates the need for "mutable" too.

BUG=302024
==========

to

==========
Move self-collapse checking to LayoutBlockFlow and cache it completely.

Only block containers (that's LayoutBlockFlow in Blinquese) can have adjoining
top and bottom margins, since all other LayoutBlock derivates establish some
kind of formatting context (table, flexbox, etc.).

Also cache self-collapsedness completely. Previously we only used the cached
result if we had previously found that the entire subtree is self-collapsing.
The new approach eliminates the need for "mutable" too.

BUG=302024

Committed: https://crrev.com/43862543cb7622a39c6fbc7895ffe03ba5337f54
Cr-Commit-Position: refs/heads/master@{#390729}
==========