re-land fix #27110 with proper DDC side of changes

pkg/analyzer/test/src/task/strong/non_null_checker_test.dart

 // Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 // These tests are for an experimental feature that treats Dart primitive types
 // (int, bool, double, etc.) as non-nullable. This file is not evidence for an
 // intention to officially support non-nullable primitives in Dart (or general
 // NNBD, for that matter) so don't get too crazy about it.
 
 library analyzer.test.src.task.non_null_primitives.checker_test;
@@ skipping 93 matching lines @@
   }
 }
 ''');
   }
 
   void test_compoundAssignment() {
     addFile('''
 void main() {
   int i = 1;
   i += 2;
-  /*error:STATIC_TYPE_ERROR*/i += null;
+  /*error:INVALID_ASSIGNMENT*/i += null;
   print(i);
 }
 ''');
     check(nonnullableTypes: <String>['dart:core,int']);
   }
 
   void test_forEach() {
     addFile('''
 void main() {
   var ints = <num>[1, 2, 3, null];
@@ skipping 181 matching lines @@
   legs.insert("goat", 4);
   legs.insert("chicken", 2);
 
   int x = legs.get("goat"); // This should not produce an error.
   int y = legs.get("sheep"); // TODO(stanm): Runtime error here.
 }
 ''');
     check(nonnullableTypes: <String>['dart:core,int']);
   }
 }