code: function(propertyNames) {
        for (var name in propertyNames) {
          // Check if the name is in our blacklist.
          if (this.propertyNameBlacklist[name]) {
            console.warn('Cannot define property "' + name + '" for element "' +
              this.name + '" because it has the same name as an HTMLElement ' +
              'property, and not all browsers support overriding that. ' +
              'Consider giving it a different name.');
            // Remove the invalid accessor from the list.
            delete propertyNames[name];
          }
        }
      }
docs: Publishing/computing a property where the name might conflict with a browser property is not currently supported to help users of Polymer avoid browser bugs:  https://code.google.com/p/chromium/issues/detail?id=43394 https://bugs.webkit.org/show_bug.cgi?id=49739  We can lift this restriction when those bugs are fixed.