Don't report redundant type errors in strong mode.

pkg/analyzer/test/src/task/dart_test.dart

Index: pkg/analyzer/test/src/task/dart_test.dart
diff --git a/pkg/analyzer/test/src/task/dart_test.dart b/pkg/analyzer/test/src/task/dart_test.dart
index d98ceed2f45bd0ab00799f54c40167330d584dc1..43e01d466b146fca655f9497255721f2bacee6dc 100644
--- a/pkg/analyzer/test/src/task/dart_test.dart
+++ b/pkg/analyzer/test/src/task/dart_test.dart
@@ -4760,10 +4760,9 @@ void main() {
     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