Add dummy dart:html library for documentation.

lib/html/doc/interface/Uint8ClampedArray.dart

+// 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 Uint8ClampedArray
+interface Uint8ClampedArray extends Uint8Array default _TypedArrayFactoryProvider {
+
+  Uint8ClampedArray(int length);
+
+  Uint8ClampedArray.fromList(List<int> list);
+
+  Uint8ClampedArray.fromBuffer(ArrayBuffer buffer, [int byteOffset, int length]);
+
+  /** @domName Uint8ClampedArray.length */
+  final int length;
+
+  /** @domName Uint8ClampedArray.setElements */
+  void setElements(Object array, [int offset]);
+
+  /** @domName Uint8ClampedArray.subarray */
+  Uint8ClampedArray subarray(int start, [int end]);
+}