Add enumerations for compressed (E)AC3 sample format

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}
12 files changed