Including string.h in base.h causes any file that includes a BoringSSL
header to include string.h. Generally this wouldn't be a problem,
although string.h might slow down the compile if it wasn't otherwise
needed. However, it also causes problems for ipsec-tools in Android
because OpenSSL didn't have this behaviour.

This change removes string.h from base.h and, instead, adds it to each
.c file that requires it.

Change-Id: I5968e50b0e230fd3adf9b72dd2836e6f52d6fb37
Reviewed-on: https://boringssl-review.googlesource.com/3200
Reviewed-by: David Benjamin <davidben@chromium.org>
Reviewed-by: Adam Langley <agl@google.com>

write_quota should only be decremented by 1 in datagram mode, otherwise we'll
underflow and always allow writes through. This does not cause any existing
tests to fail.

(It will be useful once the bug in dtls1_do_write is fixed.)

Change-Id: I42aa001d7264790a3726269890635f679497fb1c
Reviewed-on: https://boringssl-review.googlesource.com/2831
Reviewed-by: Adam Langley <agl@google.com>

Change-Id: I7407261bdb2d788c879f2e67e617a615d9ff8f8b
Reviewed-on: https://boringssl-review.googlesource.com/1505
Reviewed-by: Adam Langley <agl@google.com>

Add a framework for testing the asynchronous codepath. Move some handshake
state machine coverage tests to cover a range of record-layer and
handshake-layer asynchronicity.

This adds tests for the previous two async bugs fixed.

Change-Id: I422ef33ba3eeb0ad04766871ed8bc59b677b169e
Reviewed-on: https://boringssl-review.googlesource.com/1410
Reviewed-by: Adam Langley <agl@google.com>