Implement seekToTime that guarantees that the bits save to the disk in the proper order

[tsheaff]

I'm not aware of good documentation on what order the bits will stream to resourceLoader:shouldWaitForLoadingOfRequestedResource:

I left a comment in the code about this here

So right now I believe it's only guaranteed to work if you only ever seek back rather than forward. I believe large forward seeks allow the OS to never fetch any of the bits that occurred in the middle. Anyone have more domain expertise on how the system handles seeks?