Add default code reviewers into OWNERS

Bug: 33166666
Test: gerrit uploader
Change-Id: I29a0639cbbb9628d602bc44b04d9c05e7791b04b
diff --git a/OWNERS b/OWNERS
new file mode 100644
index 0000000..eb615cc
--- /dev/null
+++ b/OWNERS
@@ -0,0 +1,4 @@
+# Default code reviewers picked from top 3 or more developers.
+# Please update this list if you find better candidates.
+ghartman@google.com
+haining@google.com