Add Steven Thomas to libs/gui/OWNERS

Bug: n/a
Test: n/a
diff --git a/libs/gui/OWNERS b/libs/gui/OWNERS
index 73150dc..274153c 100644
--- a/libs/gui/OWNERS
+++ b/libs/gui/OWNERS
@@ -4,4 +4,5 @@
 marissaw@google.com
 mathias@google.com
 racarr@google.com
+steventhomas@google.com
 stoza@google.com