Add dummy dart:html library for documentation.

lib/html/doc/interface/MediaKeyError.dart

Index: lib/html/doc/interface/MediaKeyError.dart
diff --git a/lib/html/doc/interface/MediaKeyError.dart b/lib/html/doc/interface/MediaKeyError.dart
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index 0000000000000000000000000000000000000000..282dd762bb5b9ffde25576afde4e2c7be993b28a
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+++ b/lib/html/doc/interface/MediaKeyError.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 MediaKeyError
+interface MediaKeyError {
+
+  static final int MEDIA_KEYERR_CLIENT = 2;
+
+  static final int MEDIA_KEYERR_DOMAIN = 6;
+
+  static final int MEDIA_KEYERR_HARDWARECHANGE = 5;
+
+  static final int MEDIA_KEYERR_OUTPUT = 4;
+
+  static final int MEDIA_KEYERR_SERVICE = 3;
+
+  static final int MEDIA_KEYERR_UNKNOWN = 1;
+
+  /** @domName MediaKeyError.code */
+  final int code;
+}