Do not allow native syntax on all libraries.

dart/frog/leg/native_handler.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('native');
 #import('../../lib/uri/uri.dart');
 #import('leg.dart');
 #import('elements/elements.dart');
 #import('scanner/scannerlib.dart');
 #import('ssa/ssa.dart');
@@ skipping 13 matching lines @@
         // otherwise it will only be parsed if there is a call to
         // one of its constructor.
         element.parseNode(compiler);
         // Resolve to setup the inheritance.
         element.resolve(compiler);
       }
     }
   }
 }
 
-void checkNativeSupport(Compiler compiler,
+void maybeEnableNative(Compiler compiler,
                         LibraryElement library,
                         Uri uri) {
   String libraryName = uri.toString();
   if (library.script.name.contains('dart/frog/tests/native/src')
       || libraryName == 'dart:dom'
       || libraryName == 'dart:html') {
     library.define(new ForeignElement(
         const SourceString('native'), library), compiler);
+    library.canUseNative = true;
+  }
+}
+
+void checkAllowedLibrary(ElementListener listener, Token token) {
+  LibraryElement currentLibrary = listener.compilationUnitElement.getLibrary();
+  if (!currentLibrary.canUseNative) {
+    listener.recoverableError(token);
   }
 }
 
 Token handleNativeBlockToSkip(Listener listener, Token token) {
- token = token.next;
+  checkAllowedLibrary(listener, token);
+  token = token.next;
   if (token.kind === STRING_TOKEN) {
     token = token.next;
   }
   if (token.stringValue === '{') {
     BeginGroupToken beginGroupToken = token;
     token = beginGroupToken.endGroup;
   }
   return token;
 }
 
 Token handleNativeClassBodyToSkip(Listener listener, Token token) {
+  checkAllowedLibrary(listener, token);
   listener.handleIdentifier(token);
   token = token.next;
   if (token.kind !== STRING_TOKEN) {
     return listener.unexpected(token);
   }
   token = token.next;
   if (token.stringValue !== '{') {
     return listener.unexpected(token);
   }
   BeginGroupToken beginGroupToken = token;
   token = beginGroupToken.endGroup;
   return token;
 }
 
 Token handleNativeClassBody(Listener listener, Token token) {
+  checkAllowedLibrary(listener, token);
   token = token.next;
   if (token.kind !== STRING_TOKEN) {
     listener.unexpected(token);
   } else {
     token = token.next;
   }
   return token;
 }
 
 Token handleNativeFunctionBody(ElementListener listener, Token token) {
+  checkAllowedLibrary(listener, token);
   Token begin = token;
   listener.beginExpressionStatement(token);
   listener.handleIdentifier(token);
   token = token.next;
   if (token.kind === STRING_TOKEN) {
     listener.beginLiteralString(token);
     listener.endLiteralString(0);
     listener.pushNode(new NodeList.singleton(listener.popNode()));
     listener.endSend(token);
     token = token.next;
@@ skipping 139 matching lines @@
   } else if (!node.arguments.tail.isEmpty()) {
     builder.compiler.cancel('More than one argument to native');
   } else {
     LiteralString jsCode = node.arguments.head;
     int start = jsCode.value.slowToString()[0] === '@' ? 1 : 0;
     builder.push(new HForeign(builder.unquote(jsCode, start),
                               const SourceString('Object'),
                               <HInstruction>[]));
   }
 }