Add demux to mFrontendTests am: 86aa7010fd am: 6afaf8d190 am: 123934b067 am: 99d8ba3970

Original change: https://android-review.googlesource.com/c/platform/hardware/interfaces/+/2886926

Change-Id: Ic7c127ce51d8f26572623a133fd58cc3612b9406
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>