Do not allow native syntax on all libraries.

dart/frog/leg/elements/elements.dart

 // Copyright (c) 2012, 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('elements');
 
 #import('../tree/tree.dart');
 #import('../scanner/scannerlib.dart');
 #import('../leg.dart');  // TODO(karlklose): we only need type.
 #import('../util/util.dart');
@@ skipping 130 matching lines @@
 
 class LibraryElement extends CompilationUnitElement {
   // TODO(ahe): Library element should not be a subclass of
   // CompilationUnitElement.
 
   Link<CompilationUnitElement> compilationUnits =
     const EmptyLink<CompilationUnitElement>();
   Link<ScriptTag> tags = const EmptyLink<ScriptTag>();
   ScriptTag libraryTag;
   Map<SourceString, Element> elements;
+  bool canUseNative = false;
 
   LibraryElement(Script script)
       : elements = new Map<SourceString, Element>(),
         super.library(script);
 
   void addCompilationUnit(CompilationUnitElement element) {
     compilationUnits = compilationUnits.prepend(element);
   }
 
   void addTag(ScriptTag tag, DiagnosticListener listener) {
@@ skipping 622 matching lines @@
 
   LabelElement addLabel(Identifier label, String labelName) {
     LabelElement result = new LabelElement(label, labelName, this,
                                            enclosingElement);
     labels = labels.prepend(result);
     return result;
   }
 
   Node parseNode(DiagnosticListener l) => statement;
 }