When the display goes to sleep IDXGIOutput::WaitForVBlank returns S_OK
immediately causing the VBlankThread to consume a core entirely with the
VBlank related messaging.
To limit this problem, we use the same technique as Chromium presently
does, and we sleep for 1 ms, if the time between the last two VBlank
events was less than a ms. This limits the VBlankThread messaging rate
of about 50.000/s on an Intel 13600 to 1000/s.