Make Closure compiler happier about ShadyDOM access

Author: aomarks

lib/mixins/element-mixin.js

@@ -693,7 +693,7 @@ export const ElementMixin = dedupingMixin(base => {
             n.shadowRoot.appendChild(dom);
           }
           if (syncInitialRender && window.ShadyDOM) {
-            ShadyDOM.flushInitial(n.shadowRoot);
+            window.ShadyDOM.flushInitial(n.shadowRoot);
           }
           return n.shadowRoot;
         }

lib/utils/flattened-nodes-observer.js

@@ -152,7 +152,7 @@ export let FlattenedNodesObserver = class {
           /** @type {!NodeList<!Node>} */ (wrap(this._target).children));
       if (window.ShadyDOM) {
         this._shadyChildrenObserver =
-          ShadyDOM.observeChildren(this._target, (mutations) => {
+          window.ShadyDOM.observeChildren(this._target, (mutations) => {
             this._processMutations(mutations);
           });
       } else {
@@ -182,7 +182,7 @@ export let FlattenedNodesObserver = class {
       this._unlistenSlots(
           /** @type {!NodeList<!Node>} */ (wrap(this._target).children));
       if (window.ShadyDOM && this._shadyChildrenObserver) {
-        ShadyDOM.unobserveChildren(this._shadyChildrenObserver);
+        window.ShadyDOM.unobserveChildren(this._shadyChildrenObserver);
         this._shadyChildrenObserver = null;
       } else if (this._nativeChildrenObserver) {
         this._nativeChildrenObserver.disconnect();