Changes to JS API:
- popups have backdrop and is centered
- plugin.popup() takes a string custom element name
- plugin.popup() returns an API for closing and reopening the popup
- plugin.deprecated.popup() takes Element (similar to GWT Plugin JS API)
Recommended usage:
``` js
Gerrit.install(function(plugin) {
const popup = plugin.popup('my-plugin-popup-simple');;
// ... work
popup.close();
// ... more work
popup.open();
});
```
``` html
<dom-module id="my-plugin-popup-simple">
<template>
<div>popup popup popup popup popup </div>
</template>
<script>
Polymer({is: 'my-plugin-popup-simple'});
</script>
</dom-module>
```
Change-Id: Icb3f83d35f3c60915f12b77bc8a7d548d50d5695
2f3ee89d02