fix #27766, allow implicit casts from dynamic to composite types

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

 // Copyright (c) 2015, 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.
 
 library analyzer.test.src.task.strong.checker_test;
 
 import 'package:test_reflective_loader/test_reflective_loader.dart';
 
 import 'strong_test_helper.dart';
 
@@ skipping 970 matching lines @@
 
 dynamic x;
 
 bar1() async* { yield x; }
 Stream bar2() async* { yield x; }
 Stream<int> bar3() async* { yield /*info:DYNAMIC_CAST*/x; }
 Stream<int> bar4() async* { yield /*error:YIELD_OF_INVALID_TYPE*/new Stream<int>(); }
 
 baz1() async* { yield* /*info:DYNAMIC_CAST*/x; }
 Stream baz2() async* { yield* /*info:DYNAMIC_CAST*/x; }
-Stream<int> baz3() async* { yield* /*warning:DOWN_CAST_COMPOSITE*/x; }
+Stream<int> baz3() async* { yield* /*info:DYNAMIC_CAST*/x; }
 Stream<int> baz4() async* { yield* new Stream<int>(); }
 Stream<int> baz5() async* { yield* /*info:INFERRED_TYPE_ALLOCATION*/new Stream(); }
 ''');
   }
 
   void test_functionModifiers_syncStar() {
     checkFile('''
 dynamic x;
 
 bar1() sync* { yield x; }
 Iterable bar2() sync* { yield x; }
 Iterable<int> bar3() sync* { yield /*info:DYNAMIC_CAST*/x; }
 Iterable<int> bar4() sync* { yield /*error:YIELD_OF_INVALID_TYPE*/bar3(); }
 
 baz1() sync* { yield* /*info:DYNAMIC_CAST*/x; }
 Iterable baz2() sync* { yield* /*info:DYNAMIC_CAST*/x; }
-Iterable<int> baz3() sync* { yield* /*warning:DOWN_CAST_COMPOSITE*/x; }
+Iterable<int> baz3() sync* { yield* /*info:DYNAMIC_CAST*/x; }
 Iterable<int> baz4() sync* { yield* bar3(); }
 Iterable<int> baz5() sync* { yield* /*info:INFERRED_TYPE_ALLOCATION*/new List(); }
 ''');
   }
 
   void test_functionTypingAndSubtyping_classes() {
     checkFile('''
 class A {}
 class B extends A {}
 
@@ skipping 2976 matching lines @@
     // Regression test for https://github.com/dart-lang/sdk/issues/25069
     checkFile('''
 typedef int Foo();
 void foo() {}
 void main () {
   Foo x = /*error:INVALID_ASSIGNMENT,info:USE_OF_VOID_RESULT*/foo();
 }
 ''');
   }
 }