Let max default bitrate depend on resolution when configuring one video stream (was previously always 2Mbps).
Let max default bitrate depend on resolution when configuring one video stream (was previously always 2Mbps).

Is now set to:
<= 320x240: 600kbps
<= 640x480: 1.7Mbps
<= 960x540: 2Mbps
>  960x540: 2.5Mbps

For QVGA and VGA, the qp was around 10 at the selected thresholds when running some tests. The change in qp declined above the selected bitrates.

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

Review URL: https://codereview.webrtc.org/1297373003 .

Cr-Original-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#9878}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: 1c7d48d431e098ba42fa6bd9f1cfe69a703edee5

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