R1:da1d57b60a5f

When viewing raw file content in Differential, cache it into the File tool
before displaying it

Summary:
@alok reported a vulnerability where Flash will run carefully-crafted plain text
files.

When the user requests a raw file, cache it into Files if it isn't already
there. Then redirect them to Files. This solves the problem by executing the
SWF/TXT with CDN-domain permissions, not content-domain permissions, provided
the install is correctly configured. (Followup diff coming to make this more…