dart2js: fix type annotation

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 '../js_emitter.dart' show
     ClassStubGenerator,
     CodeEmitterTask,
     computeMixinClass,
@@ skipping 294 matching lines @@
     // the holder-instance.
     return new StaticField(element,
                            name, _registerStaticStateHolder(), code,
                            isFinal, isLazy);
   }
 
   List<StaticField> _buildStaticLazilyInitializedFields(
       LibrariesMap librariesMap) {
     JavaScriptConstantCompiler handler = backend.constants;
     DeferredLoadTask loadTask = _compiler.deferredLoadTask;
-    List<VariableElement> lazyFields = handler
+    Iterable<VariableElement> lazyFields = handler
         .getLazilyInitializedFieldsForEmission()
         .where((element) =>
             loadTask.outputUnitForElement(element) == librariesMap.outputUnit);
     return Elements.sortedByPosition(lazyFields)
         .map(_buildLazyField)
         .where((field) => field != null)  // Happens when the field was unused.
         .toList(growable: false);
   }
 
   StaticField _buildLazyField(Element element) {
@@ skipping 685 matching lines @@
       Constant constant = new Constant(name, holder, constantValue);
       _constants[constantValue] = constant;
     }
   }
 
   Holder _registerStaticStateHolder() {
     return _registry.registerHolder(
         namer.staticStateHolder, isStaticStateHolder: true);
   }
 }