See also https://bugs.chromium.org/p/chromium/issues/detail?id=862028.

There is currently no integration test to verify that selecting the correct one out of two cameras based on providing a FacingMode in the getUserMedia constraints works as expected.

If should be possible to set up a content_browsertest case that uses two fake devices and that verifies that the correct fake device gets selected by matching the device display name against an expected string.