Add tests for quality scaling.

Tests:
- Adapts down due to high QP.
- Adapts down initially due to low bitrate.

Bug: webrtc:9169
Change-Id: Ifcfc07ef6860d4dc3ede54333a56ba313e2f09d5
Reviewed-on: https://webrtc-review.googlesource.com/73160
Commit-Queue: Åsa Persson <asapersson@webrtc.org>
Reviewed-by: Rasmus Brandt <brandtr@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#23108}
diff --git a/video/BUILD.gn b/video/BUILD.gn
index 978d46e..b3213f6 100644
--- a/video/BUILD.gn
+++ b/video/BUILD.gn
@@ -343,6 +343,7 @@
       "overuse_frame_detector_unittest.cc",
       "payload_router_unittest.cc",
       "picture_id_tests.cc",
+      "quality_scaling_tests.cc",
       "quality_threshold_unittest.cc",
       "receive_statistics_proxy_unittest.cc",
       "report_block_stats_unittest.cc",