Add dummy dart:html library for documentation.

lib/html/doc/interface/WebGLDebugShaders.dart

Index: lib/html/doc/interface/WebGLDebugShaders.dart
diff --git a/lib/html/doc/interface/WebGLDebugShaders.dart b/lib/html/doc/interface/WebGLDebugShaders.dart
new file mode 100644
index 0000000000000000000000000000000000000000..1532b12f65329b455733ea1059ac9d6cbba058a8
--- /dev/null
+++ b/lib/html/doc/interface/WebGLDebugShaders.dart
@@ -0,0 +1,12 @@
+// 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 WebGLDebugShaders
+interface WebGLDebugShaders {
+
+  /** @domName WebGLDebugShaders.getTranslatedShaderSource */
+  String getTranslatedShaderSource(WebGLShader shader);
+}