Make testCancelAndResumeFetchToFile more resilient to race conditions
Make testCancelAndResumeFetchToFile more resilient to race conditions

Wait specifically for the resume data callback, which is invoked on the client's
callback queue, to come through.

google/gtm-session-fetcher,google/gtm-session-fetcher,thomasvl/gtm-session-fetcher,thomasvl/gtm-session-fetcher,thomasvl/gtm-session-fetcher,google/gtm-session-fetcher