update elements and fix some bugs

lib/src/iron-media-query/iron-media-query.html

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 <link rel="import" href="../polymer/polymer.html">
@@ skipping 30 matching lines @@
         readOnly: true,
         notify: true
       },
 
       /**
        * The CSS media query to evaluate.
        */
       query: {
         type: String,
         observer: 'queryChanged'
+      },
+      
+      /**
+       * @type {function(MediaQueryList)}
+       */ 
+      _boundMQHandler: {
+        value: function() {
+          return this.queryHandler.bind(this);
+        }
+      },
+      
+      /**
+       * @type {MediaQueryList}
+       */ 
+      _mq: {
+        value: null
       }
-
     },
 
-    created: function() {
-      this._mqHandler = this.queryHandler.bind(this);
+    attached: function() {
+      this.queryChanged();
     },
 
-    queryChanged: function(query) {
+    detached: function() {
+      this._remove();
+    },
+
+    _add: function() {
       if (this._mq) {
-        this._mq.removeListener(this._mqHandler);
+        this._mq.addListener(this._boundMQHandler);
+      }
+    },
+
+    _remove: function() {
+      if (this._mq) {
+        this._mq.removeListener(this._boundMQHandler);
+      }
+      this._mq = null;
+    },
+
+    queryChanged: function() {
+      this._remove();
+      var query = this.query;
+      if (!query) {
+        return;
       }
       if (query[0] !== '(') {
         query = '(' + query + ')';
       }
       this._mq = window.matchMedia(query);
-      this._mq.addListener(this._mqHandler);
+      this._add();
       this.queryHandler(this._mq);
     },
 
     queryHandler: function(mq) {
       this._setQueryMatches(mq.matches);
     }
 
   });
 
 </script>