This CL is part of enabling (E)AC3 passthrough feature. The new
enumerations indicate that the audio output is compressed (E)AC3
bitstream instead of PCM samples.

BUG=613385
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:linux_optional_gpu_tests_rel;master.tryserver.chromium.mac:mac_optional_gpu_tests_rel;master.tryserver.chromium.win:win_optional_gpu_tests_rel

Review-Url: https://codereview.chromium.org/2503233003
Cr-Commit-Position: refs/heads/master@{#433420}