Fix Coro.Sleep test for opt builds

Summary:
Optimized builds of //folly/experimental/coro test Coro.Sleep
would almost always fail because the compiler would generate
code that would only sleep for 0.98 seconds. Perform some
simple rounding in order to ignore slight optimizations like
these.

Reviewed By: wqfish

Differential Revision: D7496416

fbshipit-source-id: f81ff30922fbf3e5d2086fde50f4a469bdf72e51

folly/experimental/coro/test/CoroTest.cpp

@@ -18,6 +18,7 @@
 
 #if FOLLY_HAS_COROUTINES
 
+#include <folly/Chrono.h>
 #include <folly/executors/ManualExecutor.h>
 #include <folly/experimental/coro/Future.h>
 #include <folly/io/async/ScopedEventBaseThread.h>
@@ -82,8 +83,13 @@ TEST(Coro, Sleep) {
 
   future.wait();
 
+  // The total time should be roughly 1 second. Some builds, especially
+  // optimized ones, may result in slightly less than 1 second, so we perform
+  // rounding here.
+  auto totalTime = std::chrono::steady_clock::now() - startTime;
   EXPECT_GE(
-      std::chrono::steady_clock::now() - startTime, std::chrono::seconds{1});
+      chrono::round<std::chrono::seconds>(totalTime), std::chrono::seconds{1});
+
   EXPECT_TRUE(future.await_ready());
 }