Handle factory attributes consistently

This change applies the same approach of handling tag/streamKeys from factories like in the SmoothStreaming and Hls factories. It is functionally equivalent but improves readability.

PiperOrigin-RevId: 313771318

library/dash/src/main/java/com/google/android/exoplayer2/source/dash/DashMediaSource.java

@@ -376,15 +376,21 @@ public final class DashMediaSource extends BaseMediaSource {
         manifestParser = new DashManifestParser();
       }
       List<StreamKey> streamKeys =
-          !mediaItem.playbackProperties.streamKeys.isEmpty()
-              ? mediaItem.playbackProperties.streamKeys
-              : this.streamKeys;
+          mediaItem.playbackProperties.streamKeys.isEmpty()
+              ? this.streamKeys
+              : mediaItem.playbackProperties.streamKeys;
       if (!streamKeys.isEmpty()) {
         manifestParser = new FilteringManifestParser<>(manifestParser, streamKeys);
       }
-      if (mediaItem.playbackProperties.tag == null && tag != null) {
+
+      boolean needsTag = mediaItem.playbackProperties.tag == null && tag != null;
+      boolean needsStreamKeys =
+          mediaItem.playbackProperties.streamKeys.isEmpty() && !streamKeys.isEmpty();
+      if (needsTag && needsStreamKeys) {
         mediaItem = mediaItem.buildUpon().setTag(tag).setStreamKeys(streamKeys).build();
-      } else if (mediaItem.playbackProperties.streamKeys.isEmpty() && !streamKeys.isEmpty()) {
+      } else if (needsTag) {
+        mediaItem = mediaItem.buildUpon().setTag(tag).build();
+      } else if (needsStreamKeys) {
         mediaItem = mediaItem.buildUpon().setStreamKeys(streamKeys).build();
       }
       return new DashMediaSource(