Export DomRepeat from Polymer to facilitate closure validation checks

polymer_bundled.min.js file size increased by 10 bytes.

Fixed: 1147095
Change-Id: Ic56ea90e44aff3aca19701db461451af93c1e978
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2527185
Commit-Queue: Roman Arora <romanarora@chromium.org>
Reviewed-by: dpapad <dpapad@chromium.org>
Cr-Commit-Position: refs/heads/master@{#825407}

third_party/polymer/v3_0/polymer.js

@@ -11,6 +11,7 @@ subject to an additional IP rights grant found at http://polymer.github.io/PATEN
 import * as gestures from './lib/utils/gestures.js';
 
 export {DomIf} from './lib/elements/dom-if.js';
+export {DomRepeat} from './lib/elements/dom-repeat.js';
 export {mixinBehaviors} from './lib/legacy/class.js';
 export {OptionalMutableDataBehavior} from './lib/legacy/mutable-data-behavior.js';
 export {Polymer} from './lib/legacy/polymer-fn.js';