Add ACTIVITY_SECURITY_OWNERS.

Change-Id: I193ec755f720774183d3db184e511020f16dc1f6
diff --git a/ACTIVITY_SECURITY_OWNERS b/ACTIVITY_SECURITY_OWNERS
new file mode 100644
index 0000000..c39842e
--- /dev/null
+++ b/ACTIVITY_SECURITY_OWNERS
@@ -0,0 +1,2 @@
+haok@google.com
+wnan@google.com
\ No newline at end of file