dart2js: don't emit unneeded native info.

pkg/compiler/lib/src/js_emitter/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 'js_emitter.dart' show computeMixinClass;
 import 'model.dart';
 
 import '../common.dart';
@@ skipping 99 matching lines @@
     MainFragment mainFragment = _buildMainFragment(_registry.mainLibrariesMap);
     Iterable<Fragment> deferredFragments =
         _registry.deferredLibrariesMap.map(_buildDeferredFragment);
 
     List<Fragment> fragments = new List<Fragment>(_registry.librariesMapCount);
     fragments[0] = mainFragment;
     fragments.setAll(1, deferredFragments);
 
     _markEagerClasses();
 
-    bool containsNativeClasses =
-        nativeClasses.length != _unneededNativeClasses.length;
+    List<Holder> holders = _registry.holders.toList(growable: false);
 
-    List<Holder> holders = _registry.holders.toList(growable: false);
+    bool needsNativeSupport = _compiler.enqueuer.codegen.nativeEnqueuer
+        .hasInstantiatedNativeClasses();
+
+    assert(!needsNativeSupport || nativeClasses.isNotEmpty);
 
     return new Program(
         fragments,
         holders,
         _buildLoadMap(),
         _buildTypeToInterceptorMap(),
         _task.metadataCollector,
-        outputContainsNativeClasses: containsNativeClasses,
+        needsNativeSupport: needsNativeSupport,
         outputContainsConstantList: _task.outputContainsConstantList,
         hasIsolateSupport: _compiler.hasIsolateSupport);
   }
 
   void _markEagerClasses() {
     _markEagerInterceptorClasses();
   }
 
   /// Builds a map from loadId to outputs-to-load.
   Map<String, List<Fragment>> _buildLoadMap() {
@@ skipping 611 matching lines @@
       _registry.registerConstant(outputUnit, constantValue);
       assert(!_constants.containsKey(constantValue));
       String name = namer.constantName(constantValue);
       String constantObject = namer.globalObjectForConstant(constantValue);
       Holder holder = _registry.registerHolder(constantObject);
       Constant constant = new Constant(name, holder, constantValue);
       _constants[constantValue] = constant;
     }
   }
 }