Make GetLocalFileCopy pool counter call from tiff be generic

I was to make PagedTiffHandler subclass TransformationalImageHandler.
The biggest thing that's different is the pool counter call.
However, given that a file is just as expensive in terms of
network bandwidth regardless of its type, seems to make sense
to make this check generic.

Change-Id: I7e4a4769edaa4742803df407b9c719c54fb77de3