Add wala@chromium.org to owners list

BUG= none
R=stichnot@chromium.org

Review URL: https://codereview.chromium.org/305973005
diff --git a/OWNERS b/OWNERS
index a3f938a..e114c22 100644
--- a/OWNERS
+++ b/OWNERS
@@ -6,3 +6,4 @@
 mseaborn@chromium.org
 sehr@chromium.org
 stichnot@chromium.org
+wala@chromium.org