Create an outline of metadata API in dart2js.

dart/lib/compiler/implementation/compiler.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.
 
 
 /**
  * If true, print a warning for each method that was resolved, but not
  * compiled.
  */
 final bool REPORT_EXCESS_RESOLUTION = false;
@@ skipping 422 matching lines @@
       } else {
         patchMember(originalElement, patchElement);
       }
       patches = patches.tail;
     }
   }
 
   bool isPatchElement(Element element) {
     // TODO(lrn): More checks needed if we introduce metadata for real.
     // In that case, it must have the identifier "native" as metadata.
-    return !element.metadata.isEmpty();
+    for (Link link = element.metadata; !link.isEmpty(); link = link.tail) {
+      if (link.head is PatchMetadataAnnotation) return true;
+    }
+    return false;
   }
 
   Element clonePatch(Element patchElement, Element enclosing) {
     // The original library does not have an element with the same name
     // as the patch library element.
     // In this case, the patch library element must not be marked as "patch",
     // and its name must make it private.
     if (!patchElement.name.isPrivate()) {
       internalError("Cannot add non-private member '"
                     "${patchElement.name.slowToString()}' from patch.");
@@ skipping 445 matching lines @@
     final endOffset = end.charOffset + end.slowCharCount;
 
     // [begin] and [end] might be the same for the same empty token. This
     // happens for instance when scanning '$$'.
     assert(endOffset >= beginOffset);
     return f(beginOffset, endOffset);
   }
 
   String toString() => 'SourceSpan($uri, $begin, $end)';
 }