Create an outline of metadata API in dart2js.

dart/lib/compiler/implementation/patch_parser.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("patchparser");
 #import("dart:uri");
 
 #import("tree/tree.dart", prefix: "tree");
 #import("leg.dart", prefix: 'leg');  // CompilerTask, Compiler.
 #import("apiimpl.dart");
@@ skipping 128 matching lines @@
       return super.parseMember(token);
     }
     Token patch = token;
     patchListener.beginPatch(patch);
     token = super.parseMember(token.next);
     patchListener.endPatch(patch);
     return token;
   }
 }
 
-
 /**
  * Partial parser for patch files that also handles the members of class
  * declarations.
  */
 class PatchClassElementParser extends PatchParser {
   PatchClassElementParser(PatchListener listener) : super(listener);
 
   Token parseClassBody(Token token) => fullParseClassBody(token);
 }
 
-
 /**
  * Extension of [ElementListener] for parsing patch files.
  */
 class PatchElementListener extends ElementListener implements PatchListener {
   final LinkBuilder<tree.ScriptTag> imports;
   bool isMemberPatch = false;
   bool isClassPatch = false;
 
   PatchElementListener(leg.DiagnosticListener listener,
                        CompilationUnitElement patchElement,
                        int idGenerator(),
                        this.imports)
     : super(listener, patchElement, idGenerator);
 
+  MetadataAnnotation popMetadata() {
+    // TODO(ahe): Remove this method.
+    popNode(); // Discard null.
+    return new PatchMetadataAnnotation();
+  }
+
   void beginPatch(Token token) {
     if (token.next.stringValue === "class") {
       isClassPatch = true;
     } else {
       isMemberPatch = true;
     }
     handleIdentifier(token);
   }
 
   void endPatch(Token token) {
@@ skipping 11 matching lines @@
   bool allowScriptTags() => true;
 
   void addScriptTag(tree.ScriptTag tag) {
     super.addScriptTag(tag);
     imports.addLast(tag);
   }
 
   void pushElement(Element element) {
     if (isMemberPatch || (isClassPatch && element is ClassElement)) {
       // Apply patch.
-      element.addMetadata(popNode());
+      element.addMetadata(popMetadata());
       LibraryElement library = compilationUnitElement.getLibrary();
       Element existing = library.localLookup(element.name);
       if (isMemberPatch) {
         if (element is! FunctionElement) {
           listener.internalErrorOnElement(element,
                                           "Member patch is not a function.");
         }
         if (existing.kind === ElementKind.ABSTRACT_FIELD) {
           if (!element.isAccessor()) {
             listener.internalErrorOnElement(
@@ skipping 27 matching lines @@
               element, "Patching the same class more than once.");
         }
         classElement.patch = element;
       }
       return;
     }
     super.pushElement(element);
   }
 }
 
-
 /**
  * Extension of [MemberListener] for parsing patch class bodies.
  */
 class PatchMemberListener extends MemberListener implements PatchListener {
   bool isMemberPatch = false;
   bool isClassPatch = false;
   PatchMemberListener(leg.DiagnosticListener listener,
                       Element enclosingElement)
     : super(listener, enclosingElement);
 
+  MetadataAnnotation popMetadata() {
+    // TODO(ahe): Remove this method.
+    popNode(); // Discard null.
+    return new PatchMetadataAnnotation();
+  }
+
   void beginPatch(Token token) {
     if (token.next.stringValue === "class") {
       isClassPatch = true;
     } else {
       isMemberPatch = true;
     }
     handleIdentifier(token);
   }
 
   void endPatch(Token token) {
     if (token.next.stringValue === "class") {
       isClassPatch = false;
     } else {
       isMemberPatch = false;
     }
   }
 
   void addMember(Element element) {
     if (isMemberPatch || (isClassPatch && element is ClassElement)) {
-      element.addMetadata(popNode());
+      element.addMetadata(popMetadata());
     }
     super.addMember(element);
   }
 }
+
+// TODO(ahe): Get rid of this class.
+class PatchMetadataAnnotation extends MetadataAnnotation {
+  final Constant value = null;
+}