Fix warnings on implicit casts

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.
 
 // TODO(jmesserly): this file needs to be refactored, it's a port from
 // package:dev_compiler's tests
 /// General type checking tests
 library test.src.task.strong.checker_test;
 
 import 'package:unittest/unittest.dart';
@@ skipping 966 matching lines @@
           lOfOs = mOfAs;
           lOfOs = lOfDs;
           lOfOs = lOfOs;
           lOfOs = lOfAs;
         }
         {
           lOfAs = /*warning:DownCastComposite*/mOfDs;
           lOfAs = /*severe:StaticTypeError*/mOfOs;
           lOfAs = mOfAs;
           lOfAs = /*warning:DownCastComposite*/lOfDs;
-          lOfAs = /*warning:DownCastComposite*/lOfOs;
+          lOfAs = /*info:DownCastImplicit*/lOfOs;
           lOfAs = lOfAs;
         }
         {
           mOfDs = mOfDs;
           mOfDs = mOfOs;
           mOfDs = mOfAs;
           mOfDs = /*info:DownCastImplicit*/lOfDs;
           mOfDs = /*info:DownCastImplicit*/lOfOs;
-          mOfDs = /*info:DownCastImplicit*/lOfAs;
+          mOfDs = /*warning:DownCastComposite*/lOfAs;
         }
         {
           mOfOs = mOfDs;
           mOfOs = mOfOs;
           mOfOs = mOfAs;
           mOfOs = /*info:DownCastImplicit*/lOfDs;
           mOfOs = /*info:DownCastImplicit*/lOfOs;
           mOfOs = /*severe:StaticTypeError*/lOfAs;
         }
         {
           mOfAs = /*warning:DownCastComposite*/mOfDs;
-          mOfAs = /*warning:DownCastComposite*/mOfOs;
+          mOfAs = /*info:DownCastImplicit*/mOfOs;
           mOfAs = mOfAs;
           mOfAs = /*warning:DownCastComposite*/lOfDs;
-          mOfAs = /*warning:DownCastComposite*/lOfOs;
-          mOfAs = /*warning:DownCastComposite*/lOfAs;
+          mOfAs = /*info:DownCastImplicit*/lOfOs;
+          mOfAs = /*info:DownCastImplicit*/lOfAs;
         }
 
       }
    '''
   });
 
   testChecker('Type checking literals', {
     '/main.dart': '''
           test() {
             num n = 3;
@@ skipping 1279 matching lines @@
 
         baz1() sync* { yield* (/*info:DynamicCast*/x); }
         Iterable baz2() sync* { yield* (/*info:DynamicCast*/x); }
         Iterable<int> baz3() sync* { yield* (/*warning:DownCastComposite*/x); }
         Iterable<int> baz4() sync* { yield* new Iterable<int>(); }
         Iterable<int> baz5() sync* { yield* (/*info:InferredTypeAllocation*/new Iterable()); }
     '''
     });
   });
 }