Use LibraryDependencyMirror in dartdoc.

sdk/lib/_internal/compiler/implementation/mirrors/mirrors_util.dart

Index: sdk/lib/_internal/compiler/implementation/mirrors/mirrors_util.dart
diff --git a/sdk/lib/_internal/compiler/implementation/mirrors/mirrors_util.dart b/sdk/lib/_internal/compiler/implementation/mirrors/mirrors_util.dart
index 41a085e67cb02f9a03bc9f855be234a0b88de451..07f407a59c7e8132614b759dcc9ef4bf72345db8 100644
--- a/sdk/lib/_internal/compiler/implementation/mirrors/mirrors_util.dart
+++ b/sdk/lib/_internal/compiler/implementation/mirrors/mirrors_util.dart
@@ -159,3 +159,29 @@ String stripComment(String comment) {
   }
   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;
+}