Missing clear() for pseudo invalidation sets.

Missing clear() for pseudo invalidation sets.

Missing clear in RuleFeatureSet::clear caused rules removed from shadow
trees to still affect invalidation after removal.

R=sigbjornf@opera.com
BUG=538586
Committed: https://crrev.com/91a26ed83a4e0caaf54bf0e33d84ca29ebb25317
Cr-Commit-Position: refs/heads/master@{#352278}

[rune, 2015-10-04 11:22:52]

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

[commit-bot: I haz the power, 2015-10-04 11:23:00]

Dry run: CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1368313005/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1368313005/1

[commit-bot: I haz the power, 2015-10-04 12:55:45]

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

[commit-bot: I haz the power, 2015-10-04 12:55:46]

Dry run: This issue passed the CQ dry run.

[sof, 2015-10-04 20:36:23]

The CQ bit was checked by sigbjornf@opera.com

[sof, 2015-10-04 20:36:23]

lgtm

[commit-bot: I haz the power, 2015-10-04 20:36:34]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1368313005/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1368313005/1

[commit-bot: I haz the power, 2015-10-04 20:40:38]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-10-04 20:41:18]

Patchset 1 (id:??) landed as
https://crrev.com/91a26ed83a4e0caaf54bf0e33d84ca29ebb25317
Cr-Commit-Position: refs/heads/master@{#352278}