Add kainino@ as Chrome GPU testing co-owner.

Kai has made significant contributions to the test infrastructure and
should be a co-owner of the files.

Bug: none
Change-Id: I20aa18127fb7d066c69b3d1fcdceba4ecd646be6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1578070
Reviewed-by: Zhenyao Mo <zmo@chromium.org>
Commit-Queue: Kenneth Russell <kbr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#653058}
diff --git a/content/test/gpu/OWNERS b/content/test/gpu/OWNERS
index da55168..915beea 100644
--- a/content/test/gpu/OWNERS
+++ b/content/test/gpu/OWNERS
@@ -1,4 +1,5 @@
 bajones@chromium.org
+kainino@chromium.org
 kbr@chromium.org
 ynovikov@chromium.org
 zmo@chromium.org