What's happening: TracingPullLeaseManager::StartLeaseLoop -> DefaultPullLeaseManager::StartLeaseLoop -> DefaultPullLeaseManager::ExtendLeaseLoop
What should happen: TracingPullLeaseManager::StartLeaseLoop -> DefaultPullLeaseManager::StartLeaseLoop -> TracingPullLeaseManager::ExtendLeaseLoop -> DefaultPullLeaseManager::ExtendLeaseLoop

I need to refactor this so it is like the streaming pull, the StartLeaseLoop will be a public interface and the ExtendLeaseLoop will be part of a nested class.

Example here: https://github.com/alevenberg/google-cloud-cpp/blob/8dcd1c028b7b6de5f6eb684a64bb17b0a915bcee/google/cloud/pubsub/quickstart/subscriber_pull_quickstart.cc