Move reencode logic for screenshare bitrate overshoot from generic
encoder to vp8impl.
BUG=none

Review-Url: https://codereview.webrtc.org/3011213002
Cr-Original-Commit-Position: refs/heads/master@{#19803}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: e99738174344a7d172d9391f3bd9f485b9e64d67
3 files changed