Convert DCHECK to CHECK

A compromised renderer may call AudioContextAudiblePlaybackStarted()
incorrectly.  While the DCHECK in this function is not for security, it
is not on the audio hot path so there is no performance reason to keep
it as a DCHECK instead of a CHECK.

Making it a CHECK will ensure the browser process will crash here,
reducing the attack surface.

Bug: 441315099
Change-Id: I382732e1554b0fc8a2225a93679055d50ea36e44
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6908586
Commit-Queue: Michael Wilson <mjwilson@chromium.org>
Auto-Submit: Michael Wilson <mjwilson@chromium.org>
Reviewed-by: Hongchan Choi <hongchan@chromium.org>
Commit-Queue: Hongchan Choi <hongchan@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1509724}