Use TestSimpleTaskRunner::HasPendingTask instead of GetPendingTasks().empty()
TestSimpleTaskRunner::GetPendingTasks returns a full copy of the queued
pending tasks, which is less clean, and also that prevents a refactoring
that makes tasks move-only.
This CL replaces them with an equivalent HasPendingTask to avoid the copy.
BUG=
554299
Committed:
https://crrev.com/d3dd000ce7ea4854818f23ee10c68d0c86f95565
Cr-Commit-Position: refs/heads/master@{#420034}