Can not find Element in Dynamic element.

compiler/java/com/google/dart/compiler/resolver/Elements.java

Index: compiler/java/com/google/dart/compiler/resolver/Elements.java
diff --git a/compiler/java/com/google/dart/compiler/resolver/Elements.java b/compiler/java/com/google/dart/compiler/resolver/Elements.java
index 08d2f3397e78df5fcee2606efdfcbfd5cdcf9bb8..d3e06081e34080644a06620f5b560e7c28e954f5 100644
--- a/compiler/java/com/google/dart/compiler/resolver/Elements.java
+++ b/compiler/java/com/google/dart/compiler/resolver/Elements.java
@@ -111,7 +111,10 @@ public class Elements {
   }
 
   static Element findElement(ClassElement cls, String name) {
-    return ((ClassElementImplementation) cls).findElement(name);
+    if (cls instanceof  ClassElementImplementation) {
+      return ((ClassElementImplementation) cls).findElement(name);
+    }
+    return null;
   }
 
   public static MethodElement methodFromFunctionExpression(DartFunctionExpression node,