Add write permision to VIEW intent (don't regress bahavior).
Add (already known) mimetype when creating intent.
Test: Download a CSV file to Downloads *root*.
Install Sheets from play store.
Navigate to Settings > Storage > Explore > (device name) > Download
Tap CSV file.
It should open.
NOTE: This is a (manual) cherrypick from master. Manual part necessary
as DocumentsUI has moved to a new repo in master.
a4e765f16e
Bug: 31245151
Change-Id: Ic64c655d33182e559f9645c1e173b2fe4b601d6c
3f5885918b