Create an outline of metadata API in dart2js.

dart/lib/compiler/implementation/patch_parser.dart

Index: dart/lib/compiler/implementation/patch_parser.dart
diff --git a/dart/lib/compiler/implementation/patch_parser.dart b/dart/lib/compiler/implementation/patch_parser.dart
index 4ea29b45cbeef6b9e44b3472f1f9bf186d2ef70c..227b7f40e6a1426249f30706f5310f6a9d31b728 100644
--- a/dart/lib/compiler/implementation/patch_parser.dart
+++ b/dart/lib/compiler/implementation/patch_parser.dart
@@ -146,7 +146,6 @@ class PatchParser extends PartialParser {
   }
 }
 
-
 /**
  * Partial parser for patch files that also handles the members of class
  * declarations.
@@ -157,7 +156,6 @@ class PatchClassElementParser extends PatchParser {
   Token parseClassBody(Token token) => fullParseClassBody(token);
 }
 
-
 /**
  * Extension of [ElementListener] for parsing patch files.
  */
@@ -172,6 +170,12 @@ class PatchElementListener extends ElementListener implements PatchListener {
                        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;
@@ -203,7 +207,7 @@ class PatchElementListener extends ElementListener implements PatchListener {
   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) {
@@ -251,7 +255,6 @@ class PatchElementListener extends ElementListener implements PatchListener {
   }
 }
 
-
 /**
  * Extension of [MemberListener] for parsing patch class bodies.
  */
@@ -262,6 +265,12 @@ class PatchMemberListener extends MemberListener implements PatchListener {
                       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;
@@ -281,8 +290,13 @@ class PatchMemberListener extends MemberListener implements PatchListener {
 
   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;
+}