Revert until Windows crash is debugged.

tools/dom/src/PathObserver.dart

Index: tools/dom/src/PathObserver.dart
diff --git a/tools/dom/src/PathObserver.dart b/tools/dom/src/PathObserver.dart
index 9e680660691816f94dfc9f392282dc16fa3dc2a3..bf687cb3d277ed58611e13c31259ddb84399fe14 100644
--- a/tools/dom/src/PathObserver.dart
+++ b/tools/dom/src/PathObserver.dart
@@ -72,8 +72,7 @@ class PathObserver {
     // TODO(jmesserly): if the path is empty, or the object is! Observable, we
     // can optimize the PathObserver to be more lightweight.
 
-    _values = new StreamController.multiplex(onListen: _observe,
-                                             onCancel: _unobserve);
+    _values = new StreamController(onListen: _observe, onCancel: _unobserve);
 
     if (_isValid) {
       var segments = [];