mojo: Fix mojo test on Art runtime.

mojo: Fix mojo test on Art runtime.

Due to the following bug:
https://code.google.com/p/android/issues/detail?id=76644, it is not
possible in art to create an empty buffer for address NULL. This solve
the issue by creating an empty buffer on a random address. This is not
an issue as the memory will never be accessed.

BUG=406848
R=ppi@chromium.org,yfriedman@chromium.org

Committed: https://crrev.com/a8af5943653de9ebabbca1ba6378ac4ac3017e2c
Cr-Commit-Position: refs/heads/master@{#296964}

[qsr, 2014-09-26 14:35:44]

gentle pings?

[Yaron, 2014-09-26 16:26:20]

lgtm (didn't make priority inbox for some reason)

[qsr, 2014-09-26 16:26:58]

The CQ bit was checked by qsr@chromium.org

[commit-bot: I haz the power, 2014-09-26 16:28:06]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/601163002/20001

[commit-bot: I haz the power, 2014-09-26 17:07:33]

Committed patchset #2 (id:20001) as e593699ebe2fcfeec0947c5c9a1b1cac21eb1ba7

[commit-bot: I haz the power, 2014-09-26 17:08:08]

Patchset 2 (id:??) landed as
https://crrev.com/a8af5943653de9ebabbca1ba6378ac4ac3017e2c
Cr-Commit-Position: refs/heads/master@{#296964}