Use output parameter to distinguish error from absent result

Use output parameter to distinguish error from absent result
Otherwise we'd have to probe for pending exceptions.

I'll do the same to other interceptors in follow-up CLs

BUG=chromium:495949, v8:4137
LOG=n

Committed: https://crrev.com/9a92d294f394ee3f19ccb647d148d691e5498010
Cr-Commit-Position: refs/heads/master@{#29090}

[Toon Verwaest, 2015-06-17 13:23:40]

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

[Toon Verwaest, 2015-06-17 13:23:41]

ptal

[Jakob Kummerow, 2015-06-17 13:35:24]

lgtm

[Toon Verwaest, 2015-06-17 13:38:12]

The CQ bit was checked by verwaest@chromium.org

[commit-bot: I haz the power, 2015-06-17 13:38:22]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1190023002/1

[commit-bot: I haz the power, 2015-06-17 14:06:36]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-06-17 14:06:47]

Patchset 1 (id:??) landed as
https://crrev.com/9a92d294f394ee3f19ccb647d148d691e5498010
Cr-Commit-Position: refs/heads/master@{#29090}