fix: Only expand robustness on each stream once (#8458)

Without this change, `expandRobustness` ended up running 480 times for
the stream `Angel One (multicodec, multilingual, Widevine)` with
`SW_SECURE_CRYPTO,SW_SECURE_CRYPTO,SW_SECURE_CRYPTO` set up as the
multiple robustness. With it, it only runs 44 times, which is expected
because there are 22 unique streams, and it expands `videoRobustness`
and `audioRobustness` on each.

Fixes #8408

Author: gkatsev

lib/drm/drm_engine.js

@@ -446,25 +446,32 @@ shaka.drm.DrmEngine = class {
       return newDrmInfos;
     };
 
+    const expandedStreams = new Set();
+
     for (const variant of variants) {
-      if (variant.video) {
+      if (variant.video && !expandedStreams.has(variant.video)) {
         variant.video.drmInfos =
             expandRobustness(variant.video.drmInfos,
                 'videoRobustness');
         variant.video.drmInfos =
             expandRobustness(variant.video.drmInfos,
                 'audioRobustness');
+        expandedStreams.add(variant.video);
       }
-      if (variant.audio) {
+      if (variant.audio && !expandedStreams.has(variant.audio)) {
         variant.audio.drmInfos =
             expandRobustness(variant.audio.drmInfos,
                 'videoRobustness');
         variant.audio.drmInfos =
             expandRobustness(variant.audio.drmInfos,
                 'audioRobustness');
+        expandedStreams.add(variant.audio);
       }
     }
 
+    // expandedStreams is no longer needed, so, clear it
+    expandedStreams.clear();
+
     // We should get the decodingInfo results for the variants after we filling
     // in the drm infos, and before queryMediaKeys_().
     await shaka.util.StreamUtils.getDecodingInfosForVariants(variants,