Make analyzer strong-mode clean

pkg/analyzer/test/src/context/context_test.dart

 // Copyright (c) 2014, 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.context.context_test;
 
 import 'dart:async';
 import 'dart:collection';
 
 import 'package:analyzer/dart/ast/ast.dart';
@@ skipping 320 matching lines @@
 ''');
     Source exporterSource = addSource(
         "/exporter.dart",
         r'''
 export 'lib.dart';
 ''');
     _performPendingAnalysisTasks();
     // initially: A
     {
       LibraryElement libraryElement =
-          context.getResult(exporterSource, LIBRARY_ELEMENT1) as LibraryElement;
+          context.getResult(exporterSource, LIBRARY_ELEMENT1);
       expect(libraryElement.exportNamespace.definedNames.keys,
           unorderedEquals(['A']));
     }
     // after update: B
     context.setContents(
         libSource,
         r'''
 class B {}''');
     _performPendingAnalysisTasks();
     {
       LibraryElement libraryElement =
-          context.getResult(exporterSource, LIBRARY_ELEMENT1) as LibraryElement;
+          context.getResult(exporterSource, LIBRARY_ELEMENT1);
       expect(libraryElement.exportNamespace.definedNames.keys,
           unorderedEquals(['B']));
     }
   }
 
   Future test_applyChanges_remove() {
     SourcesChangedListener listener = new SourcesChangedListener();
     context.onSourcesChanged.listen(listener.onData);
     String libAContents = r'''
 library libA;
@@ skipping 4619 matching lines @@
    * Initialize the visitor.
    */
   _ElementGatherer();
 
   @override
   void visitElement(Element element) {
     elements[element] = element;
     super.visitElement(element);
   }
 }