Make rate control and quality thresholds optional in VideoProcessorIntegrationTest.

This CL is split out from https://codereview.webrtc.org/2997283002/.

BUG=webrtc:6634

Review-Url: https://codereview.webrtc.org/3008543002
Cr-Original-Commit-Position: refs/heads/master@{#19513}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: 87f5c5a4d366da90ca8239b54e25d4d9ec6c1364
3 files changed