Add buildUpon to MediaMetadata.

PiperOrigin-RevId: 364590789

library/common/src/main/java/com/google/android/exoplayer2/MediaMetadata.java

@@ -29,6 +29,12 @@ public final class MediaMetadata implements Bundleable {
   /** A builder for {@link MediaMetadata} instances. */
   public static final class Builder {
 
+    public Builder() {}
+
+    private Builder(MediaMetadata mediaMetadata) {
+      this.title = mediaMetadata.title;
+    }
+
     @Nullable private String title;
 
     /** Sets the optional title. */
@@ -39,7 +45,7 @@ public final class MediaMetadata implements Bundleable {
 
     /** Returns a new {@link MediaMetadata} instance with the current builder values. */
     public MediaMetadata build() {
-      return new MediaMetadata(this);
+      return new MediaMetadata(/* builder= */ this);
     }
   }
 
@@ -53,6 +59,11 @@ public final class MediaMetadata implements Bundleable {
     this.title = builder.title;
   }
 
+  /** Returns a new {@link Builder} instance with the current {@link MediaMetadata} fields. */
+  public Builder buildUpon() {
+    return new Builder(/* mediaMetadata= */ this);
+  }
+
   @Override
   public boolean equals(@Nullable Object obj) {
     if (this == obj) {