Make hbos OWNER of external/wpt/webrtc/, includes import notifications.

NOTRY=True

Bug: None
Change-Id: I99e4e5580845d21dde4ce0edc5f070693c318441
Reviewed-on: https://chromium-review.googlesource.com/1142769Reviewed-by: Harald Alvestrand <hta@chromium.org>
Commit-Queue: Henrik Boström <hbos@chromium.org>
Cr-Commit-Position: refs/heads/master@{#576442}

third_party/WebKit/LayoutTests/external/wpt/webrtc/OWNERS

 # COMPONENT: Blink>WebRTC
 # WPT-NOTIFY: true
+hbos@chromium.org
 hta@chromium.org