win: clock implementation

util/misc/clock.h

Index: util/misc/clock.h
diff --git a/util/misc/clock.h b/util/misc/clock.h
index 88bdcd508c16d3bbed1def82b08b1c44c22e2306..94b46caf19ecb92d3dc029fb8b8a53b0bccc72b6 100644
--- a/util/misc/clock.h
+++ b/util/misc/clock.h
@@ -37,8 +37,10 @@ uint64_t ClockMonotonicNanoseconds();
 //! \param[in] nanoseconds The number of nanoseconds to sleep. The actual sleep
 //!     may be slightly longer due to latencies and timer resolution.
 //!
-//! This function is resilient against the underlying `nanosleep()` system call
-//! being interrupted by a signal.
+//! On POSIX, this function is resilient against the underlying `nanosleep()`
+//! system call being interrupted by a signal. On Windows, the global system
+//! timer resolution is not modified with `timeBeginPeriod()`, so the time
+//! slept will have a resolution of approximately 16ms by default.
 void SleepNanoseconds(uint64_t nanoseconds);
 
 }  // namespace crashpad