Allow on-* event handlers on <sky-element>.

sky/framework/sky-radio/sky-radio.sky

 <!--
 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 -->
 <import src="/sky/framework/sky-button/sky-button.sky" as="SkyButton" />
 
-<sky-element name="sky-radio" attributes="selected:boolean, group:string">
+<sky-element
+    name="sky-radio"
+    attributes="selected:boolean, group:string"
+    on-mouseup="handleMouseUp">
 <template>
   <style>
     :host {
       display: inline-block;
       -webkit-user-select: none;
       width: 14px;
       height: 14px;
       border-radius: 7px;
       border: 1px solid blue;
       margin: 0 5px;
@@ skipping 49 matching lines @@
       radio.selected = false;
     });
   }
 };
 
 module.exports = class extends SkyButton {
   created() {
     super.created();
 
     this.controller = null;
-
-    this.addEventListener('mouseup', function() {
-      this.selected = true;
-    });
   }
   attached() {
     super.attached();
     this.controller = RadioGroupController.forRadio(this);
     this.controller.addRadio(this);
   }
   detached() {
     super.detached();
     this.controller.removeRadio(this);
     this.controller = null;
   }
   selectedChanged(oldValue, newValue) {
     if (newValue && this.controller)
       this.controller.takeSelectionFromGroup(this);
   }
   groupChanged(oldValue, newValue) {
     if (this.selected && this.controller)
       this.controller.takeSelectionFromGroup(this);
   }
+  handleMouseUp() {
+    this.selected = true;
+  }
 }.register();
 </script>
 </sky-element>