Fix hints reported by analyzer.

pkg/compiler/lib/src/js_emitter/program_builder/program_builder.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 dart2js.js_emitter.program_builder;
 
 import '../../closure.dart' show ClosureFieldElement;
 import '../../common.dart';
 import '../../common/names.dart' show Names, Selectors;
 import '../../compiler.dart' show Compiler;
@@ skipping 163 matching lines @@
     List<Holder> holders = _registry.holders.toList(growable: false);
 
     bool needsNativeSupport =
         _compiler.enqueuer.codegen.nativeEnqueuer.hasInstantiatedNativeClasses;
 
     assert(!needsNativeSupport || nativeClasses.isNotEmpty);
 
     List<js.TokenFinalizer> finalizers = [_task.metadataCollector];
     if (backend.namer is js.TokenFinalizer) {
       var namingFinalizer = backend.namer;
-      finalizers.add(namingFinalizer);
+      finalizers.add(namingFinalizer as js.TokenFinalizer);
     }
 
     return new Program(fragments, holders, _buildLoadMap(), _symbolsMap,
         _buildTypeToInterceptorMap(), _task.metadataCollector, finalizers,
         needsNativeSupport: needsNativeSupport,
         outputContainsConstantList: collector.outputContainsConstantList,
         hasIsolateSupport: backend.hasIsolateSupport);
   }
 
   void _markEagerClasses() {
@@ skipping 792 matching lines @@
       Constant constant = new Constant(name, holder, constantValue);
       _constants[constantValue] = constant;
     }
   }
 
   Holder _registerStaticStateHolder() {
     return _registry.registerHolder(namer.staticStateHolder,
         isStaticStateHolder: true);
   }
 }