Add QP for libvpx VP8 decoder.

BUG=webrtc:6541, webrtc:7065
TBR=hta@webrtc.org

Review-Url: https://codereview.webrtc.org/2656603002
Cr-Original-Commit-Position: refs/heads/master@{#16722}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: 5fec128de94c0b2d0090de8eac692dce9aa23a80
5 files changed