Add kbr and khushalsagar as WebGraphicsContext3DProvider OWNERs.

kbr leads the WebGL and khushalsagar the OOP-raster portions of this
interface and should be able to approve changes to it.

Bug: 1063437
Change-Id: I003cd3ab137d2768ab65cf7c0aa56b91e95d3733
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2524122Reviewed-by: Chris Harrelson <chrishtr@chromium.org>
Commit-Queue: Kenneth Russell <kbr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#825511}

third_party/blink/public/platform/OWNERS

@@ -7,6 +7,8 @@ per-file *.typemap=set noparent
 per-file *.typemap=file://ipc/SECURITY_OWNERS
 
 per-file web_application_cache_*=pwnall@chromium.org
+per-file web_graphics_context_3d_provider.h=kbr@chromium.org
+per-file web_graphics_context_3d_provider.h=khushalsagar@chromium.org
 per-file web_rtc_*=hbos@chromium.org
 per-file web_media_player*=mlamouri@chromium.org