Ensure that sync cascading renders don't break the profiler

[taneliang]

From Brian's 17 July email and doc:

Make sure sync cascading renders don’t break the profiler (probably fine if the UI looks weird)

Steps

• Generate a profile with a sync cascading render.
• Ensure that the profiler does not crash.

We may want to only do this later in our development. Maybe also write a test for this.