This actually accomplishes what was discussed in the bug and marks any file with the
relevant URI flags as WebDownload, and everything else as OtherDownload.
Note that I'm using DoGetProtocolFlags in order to deal with
nsIProtocolHandlerWithDynamicFlags correctly; while just getting protocol flags
from the IO service directly would be less work, it's technically less correct.
MozReview-Commit-ID: HgD1fV98IEc
--HG--
extra : rebase_source : f114532b48dbca5c83871e61c8d04c719e3b38d1
a6e0fa62ec