Remove more type casts

pkg/analyzer/lib/src/dart/constant/utilities.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.src.dart.constant.utilities;
 
 import 'dart:collection';
 
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/ast/visitor.dart';
@@ skipping 272 matching lines @@
     super.visitRedirectingConstructorInvocation(node);
     ConstructorElement target = getConstructorImpl(node.staticElement);
     if (target != null) {
       _callback(target);
     }
     return null;
   }
 
   @override
   Object visitSimpleIdentifier(SimpleIdentifier node) {
-    Element element = node.staticElement;
-    if (element is PropertyAccessorElement) {
-      element = (element as PropertyAccessorElement).variable;
-    }
+    Element staticElement = node.staticElement;
+    Element element = staticElement is PropertyAccessorElement
+        ? staticElement.variable
+        : staticElement;
     if (element is VariableElement && element.isConst) {
       _callback(element);
     }
     return null;
   }
 
   @override
   Object visitSuperConstructorInvocation(SuperConstructorInvocation node) {
     super.visitSuperConstructorInvocation(node);
     ConstructorElement constructor = getConstructorImpl(node.staticElement);
     if (constructor != null) {
       _callback(constructor);
     }
     return null;
   }
 }