closed #5392: add priority check for schedulePerFrame() and add a ScheduleUpdatePriority test.
closed #5392: add comment for unscheduleUpdate() at schedulePerFrame()
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change comment.
Merge pull request #6944 from minggo/treat-warning-as-error

Treat warning as error on iOS and Mac
[ci skip]
Merge pull request #6928 from boyu0/bug5392_scheduleUpdate

closed #5392: add priority check for schedulePerFrame() and add a ScheduleUpdatePriority test.