Hardware VP8 encoding: Use QP as metric for resize.
Hardware VP8 encoding: Use QP as metric for resize.

Add vp8 frame header parser to get QP from vp8 bitstream.

BUG= 4273
R=glaznev@webrtc.org, marpan@google.com, pbos@webrtc.org
TBR=stefan@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/49259004

Cr-Original-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#9256}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: 98d8cf58ee8c7c7b0672ce7955313a31824d6f3a

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