feat(Ads): Allow multiple calls to requestAds in CS (#5542)

lib/ads/client_side_ad_manager.js

@@ -80,7 +80,7 @@ shaka.ads.ClientSideAdManager = class {
     this.adsRenderingSettings_ =
         adsRenderingSettings || new google.ima.AdsRenderingSettings();
 
-    this.eventManager_.listenOnce(this.adsLoader_,
+    this.eventManager_.listen(this.adsLoader_,
         google.ima.AdsManagerLoadedEvent.Type.ADS_MANAGER_LOADED, (e) => {
           this.onAdsManagerLoaded_(
               /** @type {!google.ima.AdsManagerLoadedEvent} */ (e));
@@ -119,6 +119,17 @@ shaka.ads.ClientSideAdManager = class {
         imaRequest.adTagUrl || imaRequest.adsResponse,
         'The ad tag needs to be set up before requesting ads, ' +
           'or adsResponse must be filled.');
+    // Destroy the current AdsManager, in case the tag you requested previously
+    // contains post-rolls (don't play those now).
+    if (this.imaAdsManager_) {
+      this.imaAdsManager_.destroy();
+    }
+    // Your AdsLoader will be set up on page-load. You should re-use the same
+    // AdsLoader for every request.
+    if (this.adsLoader_) {
+      // Reset the IMA SDK.
+      this.adsLoader_.contentComplete();
+    }
     this.requestAdsStartTime_ = Date.now() / 1000;
     this.adsLoader_.requestAds(imaRequest);
   }

test/ads/ad_manager_unit.js

@@ -88,6 +88,10 @@ describe('Ad manager', () => {
           requestAds(imaRequest) {
             numAdsRequested += 1;
           }
+
+          contentComplete() {
+            // Nothing
+          }
         };
         window['google'].ima.AdsLoader = mockAdsLoader;
 
@@ -102,6 +106,10 @@ describe('Ad manager', () => {
               /** @type {!google.ima.AdsManager} */ (this);
             }
 
+            destroy() {
+              // Nothing
+            }
+
             getCuePoints() {
               return [];
             }