Use LibraryDependencyMirror in dartdoc.

sdk/lib/_internal/compiler/implementation/mirrors/mirrors_util.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 mirrors_util;
 
 import 'dart:collection' show Queue, IterableBase;
 
 // TODO(rnystrom): Use "package:" URL (#4968).
 import 'mirrors.dart';
@@ skipping 141 matching lines @@
         //      * Foo
         //      */
         // as "\nFoo\n" and not as "\nFoo\n     ".
         sb.write(line);
       }
     }
     return sb.toString();
   }
   throw new ArgumentError('Invalid comment $comment');
 }
+
+/**
+ * Returns an iterable over all exports found transitively from [library].
+ */
+Iterable<LibraryDependencyMirror> getExports(LibraryMirror library) {
+  bool isExport(LibraryDependencyMirror mirror) => mirror.isExport;
+
+  List<LibraryDependencyMirror> exports = <LibraryDependencyMirror>[];
+
+  Set<LibraryMirror> seenLibrarySet = new Set<LibraryMirror>();
+  Queue<LibraryDependencyMirror> pendingExports =
+      new Queue<LibraryDependencyMirror>();
+
+  seenLibrarySet.add(library);
+  pendingExports.addAll(library.libraryDependencies.where(isExport));
+
+  while (!pendingExports.isEmpty) {
+    LibraryDependencyMirror export = pendingExports.removeFirst();
+    exports.add(export);
+    LibraryMirror target = export.targetLibrary;
+    if (!seenLibrarySet.contains(target)) {
+      pendingExports.addAll(target.libraryDependencies.where(isExport));
+    }
+  }
+  return exports;
+}