Add dummy dart:html library for documentation.

lib/html/doc/interface/DOMMimeTypeArray.dart

Index: lib/html/doc/interface/DOMMimeTypeArray.dart
diff --git a/lib/html/doc/interface/DOMMimeTypeArray.dart b/lib/html/doc/interface/DOMMimeTypeArray.dart
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index 0000000000000000000000000000000000000000..246249baae82298355534d1426931d24cf0e764c
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+++ b/lib/html/doc/interface/DOMMimeTypeArray.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 DOMMimeTypeArray
+interface DOMMimeTypeArray {
+
+  /** @domName DOMMimeTypeArray.length */
+  final int length;
+
+  /** @domName DOMMimeTypeArray.item */
+  DOMMimeType item(int index);
+
+  /** @domName DOMMimeTypeArray.namedItem */
+  DOMMimeType namedItem(String name);
+}