openh264_unittests empty dummy test added.

This will enable trybots to run this new test binary (openh264_unittests) for a future CL that adds actual test code and more to it.
In the follow-up CL OpenH264 will be pulled in (adding third_party/openh264/src) and build files and test code will be added. That CL needs the trybots to run its test code.

BUG=500605

Review URL: https://codereview.chromium.org/1394983003

Cr-Commit-Position: refs/heads/master@{#353769}
10 files changed