Add a get_random_bytes() syscall to replace the SRPC-based implementation

Add a get_random_bytes() syscall to replace the SRPC-based implementation

This will let us remove one remaining use of SRPC.

This allows us to simplify tests/random/, since it no longer needs to
link in a copy of libsrpc.

Note that this doesn't remove "SecureRandom" from the name service or
remove nacl_desc_rng.c.  I'll do that in a follow-on change in order
to keep this change smaller and easier to review.

BUG= https://code.google.com/p/nativeclient/issues/detail?id=3864
TEST= run_random_test run_random_test_irt

Committed: http://src.chromium.org/viewvc/native_client?view=rev&revision=13696

[Mark Seaborn, 2014-09-03 21:43:35]

mseaborn@chromium.org changed reviewers:
+ mcgrathr@chromium.org

[Roland McGrath, 2014-09-04 17:33:12]

lgtm

[Mark Seaborn, 2014-09-04 17:38:05]

The CQ bit was checked by mseaborn@chromium.org

[commit-bot: I haz the power, 2014-09-04 17:38:19]

CQ is trying da patch. Follow status at

https://nativeclient-status.appspot.com/cq/mseaborn@chromium.org/537543003/40001

[commit-bot: I haz the power, 2014-09-04 18:20:22]

Committed patchset #3 (id:40001) as 13696