Move TreeBoundaryCrossingScopes to StyleEngine.

Move TreeBoundaryCrossingScopes to StyleEngine.

This is split out of the work for async stylesheet updates [1], but is
also part of the work on componentized style resolving in general.

The moved resetAuthorStyle method on StyleEngine may soon be gone
altogether as it does so in [1].

The plan is that TreeBoundaryCrossingScopes will also be completely
gone when we remove support for Shadow DOM v0. For Shadow DOM v1 we can
look up the scoped resolvers for the affecting scopes directly like we
already do in StyleResolver::matchScopedRules for the pure v1 case.

The documentation of the special casing of VTT and custom pseudo
elements is updated to not suggest that these rules are handled as part
of boundary crossing scopes as the current solution is better once v0
shadows go away.

[1] https://codereview.chromium.org/1913833002

R=meade@chromium.org
BUG=567021, 401359
Committed: https://crrev.com/c65b3eb1cc989a7a13813e4ef68042ae2e030c22
Cr-Commit-Position: refs/heads/master@{#427284}

[rune, 2016-10-24 13:12:26]

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

[commit-bot: I haz the power, 2016-10-24 13:12:41]

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

[rune, 2016-10-24 13:40:08]

ptal

[commit-bot: I haz the power, 2016-10-24 15:47:50]

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

[commit-bot: I haz the power, 2016-10-24 15:47:52]

Dry run: This issue passed the CQ dry run.

[meade_UTC10, 2016-10-25 02:30:45]

lgtm

[rune, 2016-10-25 06:04:59]

The CQ bit was checked by rune@opera.com

[commit-bot: I haz the power, 2016-10-25 06:05:10]

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, 2016-10-25 06:09:01]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2016-10-25 06:10:55]

Description was changed from

==========
Move TreeBoundaryCrossingScopes to StyleEngine.

This is split out of the work for async stylesheet updates [1], but is
also part of the work on componentized style resolving in general.

The moved resetAuthorStyle method on StyleEngine may soon be gone
altogether as it does so in [1].

The plan is that TreeBoundaryCrossingScopes will also be completely
gone when we remove support for Shadow DOM v0. For Shadow DOM v1 we can
look up the scoped resolvers for the affecting scopes directly like we
already do in StyleResolver::matchScopedRules for the pure v1 case.

The documentation of the special casing of VTT and custom pseudo
elements is updated to not suggest that these rules are handled as part
of boundary crossing scopes as the current solution is better once v0
shadows go away.

[1] https://codereview.chromium.org/1913833002

R=meade@chromium.org
BUG=567021,401359
==========

to

==========
Move TreeBoundaryCrossingScopes to StyleEngine.

This is split out of the work for async stylesheet updates [1], but is
also part of the work on componentized style resolving in general.

The moved resetAuthorStyle method on StyleEngine may soon be gone
altogether as it does so in [1].

The plan is that TreeBoundaryCrossingScopes will also be completely
gone when we remove support for Shadow DOM v0. For Shadow DOM v1 we can
look up the scoped resolvers for the affecting scopes directly like we
already do in StyleResolver::matchScopedRules for the pure v1 case.

The documentation of the special casing of VTT and custom pseudo
elements is updated to not suggest that these rules are handled as part
of boundary crossing scopes as the current solution is better once v0
shadows go away.

[1] https://codereview.chromium.org/1913833002

R=meade@chromium.org
BUG=567021,401359

Committed: https://crrev.com/c65b3eb1cc989a7a13813e4ef68042ae2e030c22
Cr-Commit-Position: refs/heads/master@{#427284}
==========

[commit-bot: I haz the power, 2016-10-25 06:10:56]

Patchset 1 (id:??) landed as
https://crrev.com/c65b3eb1cc989a7a13813e4ef68042ae2e030c22
Cr-Commit-Position: refs/heads/master@{#427284}