slideshow: Switch to android::uptimeMillis

time(2) is not guaranteed to always go forward which makes
it a bit dangerous to use in loops like slideshow does.
switch to uptimeMillis which is based on clock_gettime
CLOCK_MONOTONIC which is is safe.

Change-Id: Ica1b7ee50df00fcc7bc849d7eaebe64f62434a47
1 file changed