Don't report redundant type errors in strong mode.

pkg/analyzer/test/src/task/dart_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.dart_test;
 
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/ast/token.dart';
 import 'package:analyzer/dart/ast/visitor.dart';
 import 'package:analyzer/dart/element/element.dart';
@@ skipping 4742 matching lines @@
     expect(DynamicInvoke.get(idx.target), isNotNull);
     expect(DynamicInvoke.get(idx.target), isNotNull);
     expect(DynamicInvoke.get(idx.target), isTrue);
   }
 
   void test_perform_verifyError() {
     enableStrongMode();
     AnalysisTarget source = newSource(
         '/test.dart',
         '''
-int topLevel = 3;
-class C {
-  String field = topLevel;
-}
+class A {}
+class B extends A {}
+B b = new A();
 ''');
     computeResult(new LibrarySpecificUnit(source, source), STRONG_MODE_ERRORS);
     // validate
     _fillErrorListener(STRONG_MODE_ERRORS);
 
     var errors = errorListener.errors;
     expect(errors.length, 1);
     expect(errors[0].errorCode.name, "STRONG_MODE_STATIC_TYPE_ERROR");
   }
 }
@@ skipping 192 matching lines @@
   /**
    * Fill [errorListener] with [result] errors in the current [task].
    */
   void _fillErrorListener(ResultDescriptor<List<AnalysisError>> result) {
     List<AnalysisError> errors = task.outputs[result];
     expect(errors, isNotNull, reason: result.name);
     errorListener = new GatheringErrorListener();
     errorListener.addAll(errors);
   }
 }