Support metadata on patches.

pkg/compiler/lib/src/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.
 
 /**
  * This library contains the infrastructure to parse and integrate patch files.
  *
  * Three types of elements can be patched: [LibraryElement], [ClassElement],
  * [FunctionElement]. Patches are introduced in patch libraries which are loaded
  * together with the corresponding origin library. Which libraries that are
@@ skipping 368 matching lines @@
                 Element element,
                 MetadataAnnotation annotation,
                 ConstantValue constant);
 
 
   /// Checks [element] for metadata matching the [handler]. Return a non-null
   /// annotation marker matching metadata was found.
   static checkAnnotation(Compiler compiler,
                          Element element,
                          EagerAnnotationHandler handler) {
-    for (Link<MetadataAnnotation> link = element.metadata;
-         !link.isEmpty;
-         link = link.tail) {
-      MetadataAnnotation annotation = link.head;
+    for (MetadataAnnotation annotation in element.implementation.metadata) {
       var result = handler.apply(compiler, element, annotation);
       if (result != null) {
         // TODO(johnniwinther): Perform this check in
         // [Compiler.onLibrariesLoaded].
         compiler.enqueuer.resolution.addDeferredAction(element, () {
           annotation.ensureResolved(compiler);
           handler.validate(
               compiler, element, annotation,
               compiler.constants.getConstantValue(annotation.constant));
         });
@@ skipping 188 matching lines @@
 
 class PatchVersion {
   final String tag;
 
   const PatchVersion(this.tag);
 
   bool isActive(String patchTag) => tag == null || tag == patchTag;
 
   String toString() => 'PatchVersion($tag)';
 }