Upgrade code to Polymer 1.x/2.x hybrid support (#1047)
Upgrade code to Polymer 1.x/2.x hybrid support (#1047)

See https://www.polymer-project.org/2.0/docs/upgrade#convert-template-extension-elements-at-the-document-level.
webcomponents/webcomponents.org,customelements/v2,customelements/v2,webcomponents/webcomponents.org,webcomponents/webcomponents.org,customelements/v2,customelements/v2