Steps to reproduce:
1) Open 'Theme Preferences'
Application-->Desktop Preferences-->Theme
2) Open 'gnome-terminal' and change the permission of theme folder to
'drw-rw-rw'
$ chmod 666 /home/user/.themes
2) Open 'Nautilus' and try to drag and drop any file from 'Nautilus' window
to 'Theme Preferences'.
A dialog box 'Install new theme' will pop up giving the location of new
theme to be installed as '/home/user/file'
3) Click on 'Install' button and then click on 'Go to theme folder'
   I
   It is observed that although no file get copied to theme folder but
also no
error is thrown while installing new theme despite '.theme' folder not
having ample permission to write anything.

Expected Behavior:
When the theme file cannot be written to theme folder due to any reason,
proper error message should be displayed.