anchor.diff:  
     test_deadBlock_if_debugConst_prefixedIdentifier2() async {
       newFile('/test/lib/lib2.dart', content: r'''
  -library lib2;
   class A {
     static const bool DEBUG = false;
   }''');
       await assertNoErrorsInCode(r'''
  -library L;
   import 'lib2.dart';
   f() {
     if(A.DEBUG) {}
  
positive.code: 
    test_binary_nullType() async {
      await assertNoErrorsInCode(r'''
  @pragma('analyzer:non-nullable')
  library foo;
  
  m() {
    Null x;
    x ?? 1;
  
negative.code: 
    test_deadBlock_if_debugConst_propertyAccessor() async {
      newFile('/test/lib/lib2.dart', content: r'''
  class A {
    static const bool DEBUG = false;
  }''');
      await assertNoErrorsInCode(r'''
  import 'lib2.dart' as LIB;
  f() {
    if(LIB.A.DEBUG) {}
  