fix(DASH): Prevent memory leak in uncompiled mode (#8884)

Keeping `this` references in DASH uri callbacks leads to keeping
DashParser instances in memory after unloading.
Luckily this is only the issue in uncompiled mode, Closure Compiler
handles it somehow. It is though better to fix it in case we change
tooling some day.

Author: tykus160

lib/dash/dash_parser.js

@@ -617,21 +617,22 @@ shaka.dash.DashParser = class {
         }
       }
     }
-    this.lastCalculatedBaseUris_ = null;
+    this.lastCalculatedBaseUris_.splice(0);
     if (!someLocationValid || !this.contentSteeringManager_) {
       const uris = uriObjs.map(TXml.getContents);
-      this.lastCalculatedBaseUris_ = shaka.util.ManifestParserUtils.resolveUris(
-          manifestBaseUris, uris);
+      this.lastCalculatedBaseUris_.push(
+          ...shaka.util.ManifestParserUtils.resolveUris(
+              manifestBaseUris, uris));
     }
 
+    const contentSteeringManager = this.contentSteeringManager_;
+    const lastCalculatedBaseUris = this.lastCalculatedBaseUris_;
+
     const getBaseUris = () => {
-      if (this.contentSteeringManager_ && someLocationValid) {
-        return this.contentSteeringManager_.getLocations('BaseURL');
-      }
-      if (this.lastCalculatedBaseUris_) {
-        return this.lastCalculatedBaseUris_;
+      if (contentSteeringManager && someLocationValid) {
+        return contentSteeringManager.getLocations('BaseURL');
       }
-      return [];
+      return lastCalculatedBaseUris.slice();
     };
 
     this.manifestPatchContext_.getBaseUris = getBaseUris;
@@ -2666,12 +2667,14 @@ shaka.dash.DashParser = class {
       calculatedBaseUris = uriObjs.map(TXml.getContents);
     }
 
+    const contentSteeringManager = this.contentSteeringManager_;
+
     const getFrameUris = () => {
       if (!uriObjs.length) {
         return [];
       }
-      if (this.contentSteeringManager_ && someLocationValid) {
-        return this.contentSteeringManager_.getLocations(id);
+      if (contentSteeringManager && someLocationValid) {
+        return contentSteeringManager.getLocations(id);
       }
       if (calculatedBaseUris) {
         return calculatedBaseUris;