Used to distinguish between software/hardware encoders/decoders and other implementation differences. Useful for tracking quality regressions related to specific implementations. BUG=webrtc:4897 R=hta@webrtc.org, mflodman@webrtc.org, stefan@webrtc.org Review URL: https://codereview.webrtc.org/1406903002 . Cr-Commit-Position: refs/heads/master@{#11084}