Add scrolling screenshare test to full_stack perf tests.
Add scrolling screenshare test to full_stack perf tests.

BUG=
R=pbos@webrtc.org

Review URL: https://codereview.webrtc.org/1298613004 .

Cr-Original-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#9850}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: 6ee69aa94c8d3d84d6b30462e38004a465af0a7e

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