Add dummy dart:html library for documentation.

lib/html/doc/interface/Text.dart

Index: lib/html/doc/interface/Text.dart
diff --git a/lib/html/doc/interface/Text.dart b/lib/html/doc/interface/Text.dart
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index 0000000000000000000000000000000000000000..a7551866e6a75639877a6364bf5885b5980d9d61
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+++ b/lib/html/doc/interface/Text.dart
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+// Copyright (c) 2011, 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 Text
+interface Text extends CharacterData default _TextFactoryProvider {
+
+  Text(String data);
+
+  /** @domName Text.wholeText */
+  final String wholeText;
+
+  /** @domName Text.replaceWholeText */
+  Text replaceWholeText(String content);
+
+  /** @domName Text.splitText */
+  Text splitText(int offset);
+}