Add dummy dart:html library for documentation.

lib/html/doc/interface/Blob.dart

Index: lib/html/doc/interface/Blob.dart
diff --git a/lib/html/doc/interface/Blob.dart b/lib/html/doc/interface/Blob.dart
new file mode 100644
index 0000000000000000000000000000000000000000..cdcb8dc5c7a22084c1a93e8e2f930e0d70e6ffd0
--- /dev/null
+++ b/lib/html/doc/interface/Blob.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 Blob
+interface Blob {
+
+  /** @domName Blob.size */
+  final int size;
+
+  /** @domName Blob.type */
+  final String type;
+
+  /** @domName Blob.webkitSlice */
+  Blob webkitSlice([int start, int end, String contentType]);
+}