Support parameter metadata.

sdk/lib/_internal/compiler/implementation/elements/modelx.dart

 // Copyright (c) 2013, 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.modelx;
 
 import 'elements.dart';
 import '../../compiler.dart' as api;
 import '../tree/tree.dart';
 import '../util/util.dart';
@@ skipping 1122 matching lines @@
                    this.cachedNode)
     : this.variables = variables,
       super(name, kind, variables.enclosingElement);
 
   VariableElementX.synthetic(String name,
       ElementKind kind,
       Element enclosing) :
         variables = null,
         super(name, kind, enclosing);
 
+  void addMetadata(MetadataAnnotation metadata) {
+    variables.addMetadata(metadata);
+  }
+
+  Link<MetadataAnnotation> get metadata => variables.metadata;
+
   Node parseNode(DiagnosticListener listener) {
     if (cachedNode != null) return cachedNode;
     VariableDefinitions definitions = variables.parseNode(listener);
     for (Link<Node> link = definitions.definitions.nodes;
          !link.isEmpty; link = link.tail) {
       Expression initializedIdentifier = link.head;
       Identifier identifier = initializedIdentifier.asIdentifier();
       if (identifier == null) {
         identifier = initializedIdentifier.asSendSet().selector.asIdentifier();
       }
@@ skipping 1301 matching lines @@
  * there is an at-sign, '@'. The [value] of each of these instances
  * are the same compile-time constant, [: const Data() :].
  *
  * The mirror system does not have a concept matching this class.
  */
 abstract class MetadataAnnotationX implements MetadataAnnotation {
   /**
    * The compile-time constant which this annotation resolves to.
    * In the mirror system, this would be an object mirror.
    */
-  Constant get value;
+  Constant value;
   Element annotatedElement;
   int resolutionState;
 
   /**
    * The beginning token of this annotation, or [:null:] if it is synthetic.
    */
   Token get beginToken;
 
   MetadataAnnotationX([this.resolutionState = STATE_NOT_STARTED]);
 
   MetadataAnnotation ensureResolved(Compiler compiler) {
     if (resolutionState == STATE_NOT_STARTED) {
       compiler.resolver.resolveMetadataAnnotation(this);
     }
     return this;
   }
 
+  Node parseNode(DiagnosticListener listener);
+
   String toString() => 'MetadataAnnotation($value, $resolutionState)';
 }
+
+/// Metadata annotation on a parameter.
+class ParameterMetadataAnnotation extends MetadataAnnotationX {
+  final Metadata metadata;
+
+  ParameterMetadataAnnotation(Metadata this.metadata);
+
+  Node parseNode(DiagnosticListener listener) => metadata.expression;
+
+  Token get beginToken => metadata.getBeginToken();
+
+  Token get endToken => metadata.getEndToken();
+}