/// A test that async-backtrace is well-behaved under contention.
///
/// In this test, two threads are spawned:
/// 1. Thread 1 executes a `framed` future, which requests a blocking taskdump
/// three times in different ways (immediately, in a sub-frame, and upon drop).
/// 2. Thread 2 requests a blocking taskdump.
use framed;
pub async