Set correct encoder-specific settings for vpx in the new API.

Also, make VideoEncoderConfig::ContentType an enum class.

BUG=4569
R=mflodman@webrtc.org, pbos@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/46069004

Cr-Original-Commit-Position: refs/heads/master@{#9093}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: 143cec1cc68b9ba44f3ef4467f1422704f2395f0
7 files changed