Update balanced tests to use BalancedDegradationTest fixture.
Update balanced tests to use BalancedDegradationTest fixture.

Bug: none
Change-Id: If10f28ff1da40a379b4a5b26c7bdf638913b48c8
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/153351
Reviewed-by: Rasmus Brandt <9545de3a34b925a736ae2b5ee593f3033f743a28@webrtc.org>
Commit-Queue: Åsa Persson <5ff7466874d1fe71d5fe7d79a8a23f5ef50662da@webrtc.org>
Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#29312}

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