R1:a3ffab6205b2

Use JX.Request.setRawData()

Summary:
See D3727.

@paulshen, these are the only callsites we have in Phabricator so we can remove `setFile()` once it's clear on the Facebook side.

Test Plan: Uploaded a file with drag and drop.

Reviewers: paulshen, vrana, mnml0

Reviewed By: mnml0

CC: aran

Differential Revision: https://secure.phabricator.com/D3769