Clarify what APIs return Maybe and MaybeLocal values

Clarify what APIs return Maybe and MaybeLocal values

If the Maybe is nothing or the MaybeLocal is empty, it means that the
API call either threw an exception or an exception was already pending.

In that case, the embedder needs to handle the exception or otherwise
react to the failed API call.

BUG=v8:3929
R=svenpanne@chromium.org
LOG=y

Committed: https://crrev.com/5d8e3bfaffd1c0edac4f03b41767b101dd75c482
Cr-Commit-Position: refs/heads/master@{#27298}

[Sven Panne, 2015-03-19 10:20:24]

lgtm

[jochen (gone - plz use gerrit), 2015-03-19 10:21:53]

The CQ bit was checked by jochen@chromium.org

[commit-bot: I haz the power, 2015-03-19 10:22:09]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1022803002/1

[commit-bot: I haz the power, 2015-03-19 12:38:40]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-03-19 12:38:51]

Patchset 1 (id:??) landed as
https://crrev.com/5d8e3bfaffd1c0edac4f03b41767b101dd75c482
Cr-Commit-Position: refs/heads/master@{#27298}