dart2js: fix type annotation

pkg/compiler/lib/src/js_emitter/program_builder/program_builder.dart

Index: pkg/compiler/lib/src/js_emitter/program_builder/program_builder.dart
diff --git a/pkg/compiler/lib/src/js_emitter/program_builder/program_builder.dart b/pkg/compiler/lib/src/js_emitter/program_builder/program_builder.dart
index e6d06ed1416116a007bdb43a8f69e88374a9f294..42f7138c0fc414b7964ba0fe9a9c27ecd077f790 100644
--- a/pkg/compiler/lib/src/js_emitter/program_builder/program_builder.dart
+++ b/pkg/compiler/lib/src/js_emitter/program_builder/program_builder.dart
@@ -312,7 +312,7 @@ class ProgramBuilder {
       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);