use == and != to enable handling null/undefined

lib/runtime/dart_runtime.js

Index: lib/runtime/dart_runtime.js
diff --git a/lib/runtime/dart_runtime.js b/lib/runtime/dart_runtime.js
index fce2a35f9f39fdf68d3c551c75314e4e2735b10a..9e1e358331e9b4f6eb4e5e4eadcf1493243a7ce4 100644
--- a/lib/runtime/dart_runtime.js
+++ b/lib/runtime/dart_runtime.js
@@ -128,9 +128,9 @@ var dart, _js_helper;
   dart.arity = arity;
 
   function equals(x, y) {
-    if (x === null || y === null) return x === y;
+    if (x == null || y == null) return x == y;
     var eq = x['=='];
-    return eq ? eq.call(x, y) : x === y;
+    return eq ? eq.call(x, y) : x == y;
   }
   dart.equals = equals;