Add rtoy as platform OWNER.

Raymond is the primary OWNER of platform/audio and needs to be able to
approve CLs which change the top-level BUILD.gn.

BUG=778262

Change-Id: I9f3b7478e95b34187669371d894c863ff86936f2
Reviewed-on: https://chromium-review.googlesource.com/827609Reviewed-by: Ian Vollick <vollick@chromium.org>
Cr-Commit-Position: refs/heads/master@{#524465}

third_party/WebKit/Source/platform/OWNERS

@@ -11,6 +11,7 @@ mkwst@chromium.org
 noel@chromium.org
 pdr@chromium.org
 pfeldman@chromium.org
+rtoy@chromium.org
 schenney@chromium.org
 senorblanco@chromium.org
 skyostil@chromium.org