Currently, the sync socket in MojoAudioOutputStream is closed by both
Mojo and the SyncSocket destructor. This causes problems if a handle
happens to be reused.

BUG=709394
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/2809673002
Cr-Commit-Position: refs/heads/master@{#464374}