Changes made:
* VideoProcessorIntegrationTest definition goes in .h file.
* Member function definitions go into .cc file.
* Tests move to _libvpx.cc and _openh264.cc files.
BUG=webrtc:6634
Review-Url: https://codereview.webrtc.org/3008913002
Cr-Commit-Position: refs/heads/master@{#19637}