polygerrit-ui/app/samples/repo-command.html

<dom-module id="sample-repo-command">
  <script>
    Gerrit.install(plugin => {
      // High-level API
      plugin.project()
          .createCommand('Bork', (repoName, projectConfig) => {
            if (repoName !== 'All-Projects') {
              return false;
            }
          }).onTap(() => {
            alert('Bork, bork!');
          });

      // Low-level API
      plugin.registerCustomComponent(
          'repo-command', 'repo-command-low');
    });
  </script>
</dom-module>

<!-- Low-level custom component for repo command. -->
<dom-module id="repo-command-low">
  <template>
    <gr-repo-command
        title="Low-level bork"
        on-command-tap="_handleCommandTap">
    </gr-repo-command>
  </template>
  <script>
    Polymer({
      is: 'repo-command-low',

      attached() {
        console.log(this.repoName);
        console.log(this.config);
        this.hidden = this.repoName !== 'All-Projects';
      },
      _handleCommandTap() {
        alert('(softly) bork, bork.');
      },
    });
  </script>
</dom-module>