13   c2.onmessage = common.mustCall((e) => {
75   c1.onmessage = handler;
76   c2.onmessage = handler;
77   c3.onmessage = handler;
90   c2.onmessage = common.mustNotCall();
92   c3.onmessage = common.mustCall(() => c3.close());
102   c2.onmessage = common.mustNotCall();
103   c3.onmessage = common.mustCall(() => c3.close());
113   c2.onmessage = common.mustCall((e) => {
117     c3.onmessage = common.mustCall((event) => {
136     c1.onmessage = (e) => events.push('c1: ' + e.data);  function in c1
137     c2.onmessage = (e) => events.push('c2: ' + e.data);  function in c2
138     c3.onmessage = (e) => events.push('c3: ' + e.data);  function in c3