VSO_0226079_mutex is sporadically failing

[StephanTLavavej]

We encountered a sporadic test failure:

Assertion failed: time_execution([this] { unique_lock<Mutex> ul(mtx, 50ms); assert(!ul.owns_lock()); }) >= 50ms,
file C:\a\1\s\tests\std\tests\VSO_0226079_mutex\test.cpp, line 327

STL/tests/std/tests/VSO_0226079_mutex/test.cpp

Lines 324 to 327 in ea156e7

	assert(time_execution([this] {
	unique_lock<Mutex> ul(mtx, 50ms);
	assert(!ul.owns_lock());
	}) >= 50ms);

It appears that system_clock behavior may be making this test unreliable.

[CaseyCarter]

Any idea why time_execution doesn't measure with steady_clock?