Update all Angular libs (run update_all.sh).

third_party/pkg/angular/lib/formatter/stringify.dart

+part of angular.formatter_internal;
+
+/**
+ * Allows you to convert an object to a string.
+ *
+ * Null object are converted to an empty string.
+ *
+ *
+ * Usage:
+ *
+ *     {{ expression | stringify }}
+ */
+@Formatter(name:'stringify')
+class Stringify implements Function {
+  String call(obj) => obj == null ? "" : obj.toString();
+}