update elements and fix some bugs

lib/src/iron-meta/iron-meta.html

Index: lib/src/iron-meta/iron-meta.html
diff --git a/lib/src/iron-meta/iron-meta.html b/lib/src/iron-meta/iron-meta.html
index 4b3431182823c53da1630bbc5ff79ab2c5a9a49d..0d3a06e0f470f537f90839553014221390b72b0d 100644
--- a/lib/src/iron-meta/iron-meta.html
+++ b/lib/src/iron-meta/iron-meta.html
@@ -58,6 +58,7 @@ Or, in a Polymer element, you can include a meta in your template:
     // monostate data
     var metaDatas = {};
     var metaArrays = {};
+    var singleton = null;
 
     Polymer.IronMeta = Polymer({
 
@@ -110,6 +111,10 @@ Or, in a Polymer element, you can include a meta in your template:
 
       },
 
+      hostAttributes: {
+        hidden: true
+      },
+
       /**
        * Only runs if someone invokes the factory/constructor directly
        * e.g. `new Polymer.IronMeta()`
@@ -204,6 +209,13 @@ Or, in a Polymer element, you can include a meta in your template:
 
     });
 
+    Polymer.IronMeta.getIronMeta = function getIronMeta() {
+       if (singleton === null) {
+         singleton = new Polymer.IronMeta();
+       }
+       return singleton;
+     };
+
     /**
     `iron-meta-query` can be used to access infomation stored in `iron-meta`.