Merge video_engine_core into webrtc target.

Merges the two video targets since video_engine is no longer usable
standalone.

BUG=webrtc:1695
R=mflodman@webrtc.org, stefan@webrtc.org

Review URL: https://codereview.webrtc.org/1184763009.

Cr-Commit-Position: refs/heads/master@{#9479}
10 files changed