Fix cluster-fuzz regression with Workers and recursive serialization

Fix cluster-fuzz regression with Workers and recursive serialization

Shell::SerializeValue was using a HandleScope, but was also storing Handles in
an ObjectList. The ObjectList handles would persist after the function had
returned, but will have already been destroyed by the HandleScope, so there is
a use-after-free.

This change removes the HandleScope in Shell::SerializeValue and relies on the
caller's HandleScope.

BUG=chromium:503968
R=jochen@chromium.org
LOG=n

Committed: https://crrev.com/5023335b4d0d48df880480a5baf6ca601912afe8
Cr-Commit-Position: refs/heads/master@{#29265}

[jochen (gone - plz use gerrit), 2015-06-24 17:53:53]

lgtm

[binji, 2015-06-24 18:29:05]

The CQ bit was checked by binji@chromium.org

[commit-bot: I haz the power, 2015-06-24 18:29:30]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1211433003/1

[commit-bot: I haz the power, 2015-06-24 18:31:49]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-06-24 18:32:00]

Patchset 1 (id:??) landed as
https://crrev.com/5023335b4d0d48df880480a5baf6ca601912afe8
Cr-Commit-Position: refs/heads/master@{#29265}