Fix load graph test failure on Firefox 69.
Fix load graph test failure on Firefox 69.

We are seeing spurious errors from the load graph tests.  These errors
don't appear to be thrown from any of our code and I can't find what is
causing the uncaught rejection errors.  But adding a delay seems to
remove the errors.

Fixes: 140725109
Change-Id: Ia08e7a4c12a17cf5610db64b146b863c8e5ecbeb

shaka-project/shaka-player,shaka-project/shaka-player,shaka-project/shaka-player,shaka-project/shaka-player,tvoli/shaka-player,tvoli/shaka-player,tvoli/shaka-player,tvoli/shaka-player