Add dummy dart:html library for documentation.

lib/html/doc/interface/PerformanceNavigation.dart

Index: lib/html/doc/interface/PerformanceNavigation.dart
diff --git a/lib/html/doc/interface/PerformanceNavigation.dart b/lib/html/doc/interface/PerformanceNavigation.dart
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+// 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.
+
+// WARNING: Do not edit - generated code.
+
+/// @domName PerformanceNavigation
+interface PerformanceNavigation {
+
+  static final int TYPE_BACK_FORWARD = 2;
+
+  static final int TYPE_NAVIGATE = 0;
+
+  static final int TYPE_RELOAD = 1;
+
+  static final int TYPE_RESERVED = 255;
+
+  /** @domName PerformanceNavigation.redirectCount */
+  final int redirectCount;
+
+  /** @domName PerformanceNavigation.type */
+  final int type;
+}