First step towards having patch files for generic libraries.

lib/compiler/implementation/lib/web.dartp

Index: lib/compiler/implementation/lib/web.dartp
diff --git a/lib/html/doc/nodoc-src/_MediaStreamFactoryProvider.dart b/lib/compiler/implementation/lib/web.dartp
similarity index 50%
copy from lib/html/doc/nodoc-src/_MediaStreamFactoryProvider.dart
copy to lib/compiler/implementation/lib/web.dartp
index c1b61f33fbae803e18e78529a621c78be195df36..c3ba2ad9622b0b90ada24d19f384dfc46e14eba9 100644
--- a/lib/html/doc/nodoc-src/_MediaStreamFactoryProvider.dart
+++ b/lib/compiler/implementation/lib/web.dartp
@@ -2,6 +2,12 @@
 // 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.
 
-class _MediaStreamFactoryProvider {
-  factory MediaStream(MediaStreamTrackList audioTracks, MediaStreamTrackList videoTracks) => null;
+// Patch file for dart:web
+
+/*patch*/ String htmlEscape(String text) {
+  return text.replaceAll("&", "&")
+             .replaceAll("<", "&lt;")
+             .replaceAll(">", "&gt;")
+             .replaceAll('"', "&quot;")
+             .replaceAll("'", "&apos;");  // Different from original.
 }