Comment 34 for bug 1509139

Gustav is correct. Editing the file /usr/bin/xdg-settings as described in the bug report has fixed the problem for me in 15.10. Perhaps this will help someone at least eliminate the annoyance for now.

The offending line for me is line #198
command="`grep -E "^Exec(\[[^]=]*])?=" "$file" | cut -d= -f 2- | sed -e 's/ .*$//'`"

rectified to:
command="`grep -E "^Exec(\[[^]=]*])?=" "$file" | cut -d= -f 2- | sed -e 's/ .*$//' | head -n 1`"

After making this change, you can set the default browser within the Chrome settings as Nikita mentioned, and it will succeed.