Use customCacheKey in DownloadHelper.createMediaSource

Issue: #6870
PiperOrigin-RevId: 289658261

library/core/src/main/java/com/google/android/exoplayer2/offline/DownloadHelper.java

@@ -448,6 +448,7 @@ public final class DownloadHelper {
         break;
       case DownloadRequest.TYPE_PROGRESSIVE:
         return new ProgressiveMediaSource.Factory(dataSourceFactory)
+            .setCustomCacheKey(downloadRequest.customCacheKey)
             .createMediaSource(downloadRequest.uri);
       default:
         throw new IllegalStateException("Unsupported type: " + downloadRequest.type);

library/core/src/main/java/com/google/android/exoplayer2/source/ProgressiveMediaSource.java

@@ -111,7 +111,7 @@ public final class ProgressiveMediaSource extends BaseMediaSource
      * @return This factory, for convenience.
      * @throws IllegalStateException If {@link #createMediaSource(Uri)} has already been called.
      */
-    public Factory setCustomCacheKey(String customCacheKey) {
+    public Factory setCustomCacheKey(@Nullable String customCacheKey) {
       Assertions.checkState(!isCreateCalled);
       this.customCacheKey = customCacheKey;
       return this;