attributeChangedCallback(attr, oldVal, value) {
      var componentName = this.mappings[attr];
      if (attr in this.deprecatedMappings) {
        console.warn(this.deprecatedMappings[attr]);
      }
      if (!attr || !componentName) {
        super.attributeChangedCallback(attr, oldVal, value);
        return;
      }

      // Set value.
      setComponentProperty(this, componentName, value);
    }
Sync to attribute to component property whenever mapped attribute changes.
If attribute is mapped to a component property, set the component property using
the attribute value.