In https://docs.google.com/document/d/1BMduA57SojUyK89mx1xZaxRGaPJyFWg4_Qq8k7xnW14/edit?disco=AAAABquymQc&ts=5a98948a, we tried to make it so we could pass renderer-specific paramters down. However, it seems like this mechanism is insufficient: see https://chromium-review.googlesource.com/c/chromium/src/+/1117840

Let's figure out what we can do to make this work for cast.