Summary: Fixes T4241. Ref T4206. See T4241 for a description here. Generally, when we connect a fat pipe (`git-upload-pack`) to a narrow one (`git` over SSH) we currently read limitless data into memory. Instead, throttle reads until writes catch up. This is now possible because of the previous changes in this sequence. Test Plan: - Ran `git clone` and `git push` on the entire Wine repository. - Observed CPU and memory usage. - Memory usage was constant and low, CPU usage was high only during I/O (which is expected, since we have to actually do work, although thre might be room to further reduce this). Reviewers: btrahan Reviewed By: btrahan CC: aran Maniphest Tasks: T4241, T4206 Differential Revision: https://secure.phabricator.com/D7776