Add dummy dart:html library for documentation.

lib/html/doc/interface/Point.dart

Index: lib/html/doc/interface/Point.dart
diff --git a/lib/html/doc/interface/Point.dart b/lib/html/doc/interface/Point.dart
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index 0000000000000000000000000000000000000000..21a63f7d960192a905758237471cf65d8646a845
--- /dev/null
+++ b/lib/html/doc/interface/Point.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 WebKitPoint
+interface Point default _PointFactoryProvider {
+
+  Point(num x, num y);
+
+  /** @domName WebKitPoint.x */
+  num x;
+
+  /** @domName WebKitPoint.y */
+  num y;
+}