Enable plugin extension endpoints to accept and pass parameters to
plugin-provided web components.
Declare a named parameter:
``` html
<gr-endpoint-decorator name="some-endpoint">
<gr-endpoint-param name="someParam" value="[[someParam]]">
</gr-endpoint-param>
</gr-endpoint-decorator>
```
Register a component and get the parameter in the plugin:
``` js
Gerrit.install(plugin => {
plugin.registerCustomComponent(
'some-endpoint', 'my-plugin-element');
});
```
``` html
<dom-module id="my-plugin-element">
<template></template>
<script>
Polymer({
is: 'my-plugin-element',
attached() {
// Receive the parameter passed in from endpoint
console.log(this.someParam);
},
});
</script>
</dom-module>
```
Change-Id: Ie6b2d92107f332c74532e4462898ae0d876c4603
e5ec11c0c0