Implement MirrorUsed.targets for libraries

dart/sdk/lib/_internal/compiler/implementation/deferred_load.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 deferred_load;
 
 import 'dart:collection'
        show LinkedHashMap,
             LinkedHashSet;
 
@@ skipping 176 matching lines @@
       if (closure.contains(current)) continue;
       workSet.addAll(allElementsResolvedFrom(current));
       closure.add(current);
     }
     elements.addAll(closure);
   }
 
   Link<LibraryElement> findDeferredLibraries(LibraryElement library) {
     Link<LibraryElement> link = const Link<LibraryElement>();
     for (LibraryTag tag in library.tags) {
+      // TODO(ahe): This iterates over parts and exports as well, but should
+      // only iterate over imports.
       Link<MetadataAnnotation> metadata = tag.metadata;
       if (metadata == null) continue;
       for (MetadataAnnotation metadata in tag.metadata) {
         metadata.ensureResolved(compiler);
         Element element = metadata.value.computeType(compiler).element;
         if (element == deferredLibraryClass) {
           ConstructedConstant value = metadata.value;
           StringConstant nameField = value.fields[0];
           SourceString expectedName = nameField.toDartString().source;
           LibraryElement deferredLibrary = library.getLibraryFromTag(tag);
@@ skipping 33 matching lines @@
         compiler.enqueuer.resolution.getCachedElements(element);
     if (elements == null) return new LinkedHashSet<Element>();
     Node node = element.parseNode(compiler);
     if (node == null) return new LinkedHashSet<Element>();
     var collector = new DependencyCollector(elements, compiler);
     node.accept(collector);
     collector.dependencies.addAll(elements.otherDependencies);
     return collector.dependencies;
   }
 }