Add OWNERS for webaudio tests

Bug: 954593
Change-Id: I438bafec932f44a349fd0ba2e2d9910c194b9149
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1575177Reviewed-by: Hongchan Choi <hongchan@chromium.org>
Commit-Queue: Raymond Toy <rtoy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#652914}

third_party/blink/web_tests/webaudio/OWNERS

+# COMPONENT: Blink>WebAudio
+hongchan@chromium.org
+rtoy@chromium.org
\ No newline at end of file