Allow S->T <: dynamic->T

lib/src/codegen/js_codegen.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.
 
 library dev_compiler.src.codegen.js_codegen;
 
 import 'dart:collection' show HashSet;
 import 'dart:io' show Directory, File;
 
 import 'package:analyzer/analyzer.dart' hide ConstantEvaluator;
@@ skipping 161 matching lines @@
         return js.call('dart.notNull(#)', _visit(node.expression));
       } else {
         // A no-op in JavaScript.
         return _visit(node.expression);
       }
     }
 
     return _emitCast(node.expression, to);
   }
 
+  // TODO(vsm): This should go away in the future.  I'm passing in the type
+  // as a String for now to avoid breaking any existing code.  In most cases,
+  // we currently throw for function types.
+  @override
+  visitClosureWrapBase(ClosureWrapBase node) {
+    var expression = _visit(node.expression);
+    var typeString = js.escapedString(node.convertedType.toString());
+    return js.call('dart.closureWrap(#, #)', [expression, typeString]);
+  }
+
   @override
   visitAsExpression(AsExpression node) =>
       _emitCast(node.expression, node.type.type);
 
   _emitCast(Expression node, DartType type) =>
       js.call('dart.as(#)', [[_visit(node), _emitTypeName(type)]]);
 
   @override
   visitIsExpression(IsExpression node) {
     // Generate `is` as `dart.is` or `typeof` depending on the RHS type.
@@ skipping 1903 matching lines @@
 
     // TODO(jmesserly): in many cases marking the end will be unncessary.
     printer.mark(_location(node.end));
   }
 
   String _getIdentifier(AstNode node) {
     if (node is SimpleIdentifier) return node.name;
     return null;
   }
 }