Implement video region support

src/player/player-page.script.html

@@ -13,6 +13,7 @@
   let slideMarkupCache = Object.create(null);
   let templateLayoutCache = Object.create(null);
   let templateRenderPlanCache = Object.create(null);
+  let videoRegionRenderVersion = 0;
   let renderCacheViewportKey = '';
   let index = 0;
   let timer = null;