Fix DDC errors on DDC

lib/src/codegen/js_metalet.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_metalet;
 
 // TODO(jmesserly): import from its own package
 import 'package:dev_compiler/src/js/js_ast.dart';
 import 'package:dev_compiler/src/js/precedence.dart';
 
@@ skipping 114 matching lines @@
     var params = [];
     var values = [];
     var block = _build(params, values, new Block(statements));
     if (params.isEmpty) return block;
 
     var vars = [];
     for (int i = 0; i < params.length; i++) {
       vars.add(new VariableInitialization(params[i], values[i]));
     }
 
-    return new Block(
-        [new VariableDeclarationList('let', vars).toStatement(), block]);
+    return new Block(<Statement>[
+      new VariableDeclarationList('let', vars).toStatement(),
+      block
+    ]);
   }
 
   Node _build(List<TemporaryId> params, List<Expression> values, Node node) {
     // Visit the tree and count how many times each temp was used.
     var counter = new _VariableUseCounter();
     node.accept(counter);
     // Also count the init expressions.
     for (var init in variables.values) init.accept(counter);
 
     var substitutions = {};
@@ skipping 84 matching lines @@
   bool found = false;
   _IdentFinder(this.name);
 
   visitIdentifier(Identifier node) {
     if (node.name == name) found = true;
   }
   visitNode(Node node) {
     if (!found) super.visitNode(node);
   }
 }