DCHECK that audio devices are stopped prior to destruction.

This is required (and documented by a comment in the header file), so the DCHECKs are motivated.

BUG=711400
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.android:android_optional_gpu_tests_rel;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/2828233002
Cr-Commit-Position: refs/heads/master@{#466898}
4 files changed