VP9 codec controls for screensharing
VP9 codec controls for screensharing

Telling the encoder to adjust the parameters for the screen content.
Also, telling the encoder to skip the encoding of very flat/low content blocks. For now only for screensharing. (number 8 in VP8E_SET_STATIC_THRESHOLD is correct)

Review URL: https://codereview.webrtc.org/1308753006

Cr-Original-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#9860}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: 242d6384c45f9251229561552afd77d9c0e7b0b0

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