pkg/front_end/testcases/extensions/instance_tearoff.dart:54:6: Context: Write to c0@978
  c0 = new Class1(-4);
     ^
pkg/front_end/testcases/extensions/instance_tearoff.dart:58:6: Context: Write to c1@1007
  c1 = new Class1(-7);
     ^
pkg/front_end/testcases/extensions/instance_tearoff.dart:73:6: Context: Write to c0@1494
  c0 = new Class2(-4);
     ^
pkg/front_end/testcases/extensions/instance_tearoff.dart:77:6: Context: Write to c1@1523
  c1 = new Class2(-7);
     ^