perf(Ads): Reduce VMAP processing time

Author: avelad

lib/ads/interstitial_ad_manager.js

@@ -699,13 +699,13 @@ shaka.ads.InterstitialAdManager = class {
           shaka.util.Error.Category.ADS,
           shaka.util.Error.Code.VAST_INVALID_XML);
     }
+    /** @type {!Array<shaka.extern.AdInterstitial>} */
     let interstitials = [];
     if (data.tagName == 'VAST') {
       interstitials = shaka.ads.Utils.parseVastToInterstitials(
           data, this.lastTime_);
     } else if (data.tagName == 'vmap:VMAP') {
-      for (const ad of shaka.ads.Utils.parseVMAP(data)) {
-        // eslint-disable-next-line no-await-in-loop
+      const vastProcessing = async (ad) => {
         const vastResponseData = await this.makeAdRequest_(ad.uri, context);
         const vast = shaka.util.TXml.parseXml(vastResponseData, 'VAST');
         if (!vast) {
@@ -716,6 +716,13 @@ shaka.ads.InterstitialAdManager = class {
         }
         interstitials.push(...shaka.ads.Utils.parseVastToInterstitials(
             vast, ad.time));
+      };
+      const promises = [];
+      for (const ad of shaka.ads.Utils.parseVMAP(data)) {
+        promises.push(vastProcessing(ad));
+      }
+      if (promises.length) {
+        await Promise.all(promises);
       }
     }
     this.addInterstitials(interstitials);