Linux sandbox: allow sigaltstack in Android baseline policy.

Linux sandbox: allow sigaltstack in Android baseline policy.

Allow sigaltstack on Android as it is needed for thread creation.
On AARCH64, we now restrict setpriority() like on any architecture.

BUG=398611
Committed: https://crrev.com/e4654f76e0a14948e86704d6b7bc30ff1fa9b4a1
Cr-Commit-Position: refs/heads/master@{#294486}

[jln (very slow on Chromium), 2014-09-11 20:35:33]

jln@chromium.org changed reviewers:
+ mdempsky@chromium.org

[jln (very slow on Chromium), 2014-09-11 20:35:46]

Matthew: PTAL!

[mdempsky, 2014-09-11 20:36:37]

LGTM

[jln (very slow on Chromium), 2014-09-11 20:37:21]

The CQ bit was checked by jln@chromium.org

[commit-bot: I haz the power, 2014-09-11 20:39:42]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patchset/568533002/1

[commit-bot: I haz the power, 2014-09-11 23:12:37]

Committed patchset #1 (id:1) as 8eec5914de281c819e99a605f76e2739f431e3fb

[commit-bot: I haz the power, 2014-09-11 23:18:22]

Patchset 1 (id:??) landed as
https://crrev.com/e4654f76e0a14948e86704d6b7bc30ff1fa9b4a1
Cr-Commit-Position: refs/heads/master@{#294486}