Split up VideoProcessorIntegrationTest files.

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-Original-Commit-Position: refs/heads/master@{#19637}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: 12a47f696544a99c168902d87cc19dd286b6784b
5 files changed