A plugin or a site theme (gerrit-theme.html) may register a custom
Element to be inserted into this endpoint.
``` js
Gerrit.install(plugin => {
plugin.registerCustomComponent(
'header-small-banner', 'gt-header-small-banner', {replace: true});
});
```
``` html
<dom-module id="gt-header-small-banner">
<template>
<a href="http://somecode.com/">Bug Tracker</a>
</template>
<script>
Polymer({is: 'gt-header-small-banner'});
</script>
</dom-module>
````
Change-Id: Ib42550271bae27089978c5cbd81642361acdaaa2
(cherry picked from commit 09fa976ebc)
a2ff0963bf