Currently the frame capture when navigating to a page with a lot of images looks a lot like the following. Because we upload concurrently from N threads, we can end up overloading the GPU and competing with the normal frame workload.

To improve this, I'm going to force serialization of upload by posting the upload task to the io runner. This shouldn't be necessary, but we'll need some way to throttle uploads and/or avoid competing with the raster workloads before relanding support for this