Support downloading the contents of a single file "as is" from Gitiles, for
example:
https://android.googlesource.com/platform/manifest/+raw/master/default.xml
to get the raw XML rather than it wrapped inside of HTML.
This is a bit of a challenge because the server has cookies, and this is
possibly unsafe user supplied data. Raw HTML or JavaScript could cause the
user's session to be able to be hijacked.