fix warning in noSuchMethod registry

pkg/compiler/lib/src/js_backend/no_such_method_registry.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.
 
 part of js_backend;
 
 /**
  * Categorizes `noSuchMethod` implementations.
  *
  * If user code includes `noSuchMethod` implementations, type inference is
@@ skipping 190 matching lines @@
     } else if (body is Block &&
         !body.statements.isEmpty &&
         body.statements.nodes.tail.isEmpty) {
       Statement stmt = body.statements.nodes.head;
       if (stmt is Return && stmt.hasExpression) {
         expr = stmt.expression;
       }
     }
     if (expr is Send &&
         expr.isTypeCast &&
+        expr.typeAnnotationFromIsCheckOrCast.typeName is Identifier &&
         expr.typeAnnotationFromIsCheckOrCast.typeName.source == "dynamic") {
-      expr = expr.receiver;
+      expr = (expr as Send).receiver;
     }
     if (expr is Send &&
         expr.isSuperCall &&
         expr.selector is Identifier &&
         (expr.selector as Identifier).source == Identifiers.noSuchMethod_) {
       var arg = expr.arguments.head;
       if (expr.arguments.tail.isEmpty &&
           arg is Send &&
           arg.argumentsNode == null &&
           arg.receiver == null &&
@@ skipping 17 matching lines @@
       if (body.statements.nodes.head is ExpressionStatement) {
         ExpressionStatement stmt = body.statements.nodes.head;
         return stmt.expression is Throw;
       }
     }
     return false;
   }
 }
 
 enum NsmCategory { DEFAULT, THROWING, NOT_APPLICABLE, OTHER, }