[field type tracking] Fix handling of cleared WeakCells

[field type tracking] Fix handling of cleared WeakCells

Whenever a generalization is computed, the inputs must be checked for being cleared, and if they are, the generalization must be Type::Any.

Hopefully this fixes Chromium issue 527994 as well.

BUG=v8:4325, chromium:527994
LOG=n

Committed: https://crrev.com/afa60ff604bf41cacd08a8364e8a70a2b5f69d30
Cr-Commit-Position: refs/heads/master@{#30887}

[Jakob Kummerow, 2015-09-23 11:38:42]

jkummerow@chromium.org changed reviewers:
+ ulan@chromium.org

[Jakob Kummerow, 2015-09-23 11:38:43]

PTAL.

[Jakob Kummerow, 2015-09-23 11:53:05]

The CQ bit was checked by jkummerow@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2015-09-23 11:53:18]

Dry run: CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1361103002/20001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1361103002/20001

[commit-bot: I haz the power, 2015-09-23 12:17:19]

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

[commit-bot: I haz the power, 2015-09-23 12:17:19]

Dry run: This issue passed the CQ dry run.

[ulan, 2015-09-23 12:32:33]

LGTM! Good catch.

[Jakob Kummerow, 2015-09-23 12:33:29]

The CQ bit was checked by jkummerow@chromium.org

[commit-bot: I haz the power, 2015-09-23 12:33:44]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1361103002/20001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1361103002/20001

[commit-bot: I haz the power, 2015-09-23 12:35:25]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-09-23 12:43:40]

Patchset 2 (id:??) landed as
https://crrev.com/afa60ff604bf41cacd08a8364e8a70a2b5f69d30
Cr-Commit-Position: refs/heads/master@{#30887}