Originally the plan was to iterate on MCVD by starting with AVDA and
deleting/refactoring, but that didn't turn out well. The diffs were
noisy and it was a lot of work to keep it building. Now we're changing
direction and building MCVD from the ground up, taking pieces of AVDA
where necessary. It builds and comes with a minimal unittest.

BUG=660942
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:linux_optional_gpu_tests_rel;master.tryserver.chromium.mac:mac_optional_gpu_tests_rel;master.tryserver.chromium.win:win_optional_gpu_tests_rel

Review-Url: https://codereview.chromium.org/2552883003
Cr-Commit-Position: refs/heads/master@{#436733}