Handle metadata on nested function parameters.

sdk/lib/_internal/compiler/implementation/mirrors/dart2js_mirrors.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 dart2js.mirrors;
 
 import 'dart:collection' show UnmodifiableListView, UnmodifiableMapView;
 
 import '../elements/elements.dart';
 import '../scanner/scannerlib.dart';
@@ skipping 458 matching lines @@
   /// Return the compilation units comprising [library].
   static List<Mirror> compilationUnitsOf(Dart2JsLibraryMirror library) {
     return library._element.compilationUnits.toList().map(
         (cu) => new Dart2JsCompilationUnitMirror(cu, library)).toList();
   }
 
   static Iterable metadataSyntaxOf(Dart2JsElementMirror declaration) {
     Compiler compiler = declaration.mirrorSystem.compiler;
     return declaration._element.metadata.toList().map((metadata) {
       var node = metadata.parseNode(compiler);
-      Element annotatedElement = metadata.annotatedElement;
-      var context = annotatedElement.enclosingElement;
-      if (context == null) {
-        context = annotatedElement;
-      }
+      var treeElements = metadata.annotatedElement.treeElements;
       return new ResolvedNode(
-          node, context.treeElements, declaration.mirrorSystem);
+          node, treeElements, declaration.mirrorSystem);
     });
   }
 
   static ResolvedNode initializerSyntaxOf(Dart2JsFieldMirror variable) {
     var node = variable._variable.initializer;
     if (node == null) return null;
     return new ResolvedNode(
         node, variable._variable.treeElements, variable.mirrorSystem);
   }
 
   static ResolvedNode defaultValueSyntaxOf(Dart2JsParameterMirror parameter) {
     if (!parameter.hasDefaultValue) return null;
     var node = parameter._element.initializer;
-    return new ResolvedNode(node,
-        (parameter.owner as Dart2JsElementMirror)._element.treeElements,
-        parameter.mirrorSystem);
+    var treeElements = parameter._element.treeElements;
+    return new ResolvedNode(node, treeElements, parameter.mirrorSystem);
   }
 }