libchromeos: Add fake stream implementation to help with unit tests

Fake stream can offer more comprehensive testing tools when working
with streams in unit tests, compared to that of a mock stream.

Fake stream allows to simulate non-blocking reads and writes, timed
data availablity and full-fledged asynchronous operations with both
input and output data validation.

BUG=None
TEST=`FEATURES=test emerge-link libchromeos`

Change-Id: Ie3a65dc15274e66f98d8ea6d3813331cbdb08274
Reviewed-on: https://chromium-review.googlesource.com/269976
Tested-by: Alex Vakulenko <avakulenko@chromium.org>
Trybot-Ready: Alex Vakulenko <avakulenko@chromium.org>
Reviewed-by: Vitaly Buka <vitalybuka@chromium.org>
Commit-Queue: Alex Vakulenko <avakulenko@chromium.org>
4 files changed