Mike Fleetwood authored Sep 17, 2018 and Curtis Gedak committed Sep 20, 2018

Resizing a file system mounted read-only fails.  Example:

    # mkfs.btrfs /dev/sdb1
    # mount -o ro /dev/sdb1 /mnt/1

In GParted try to resize partition sdb1.  The operation fails like this:

    Grow /dev/sdb1 from 512.00 MiB to 1.00 GiB                 (ERROR)
    * calibrate /dev/sdb1                                      (SUCCESS)
    * grow partition from 512.00 MiB to 1.00 GiB               (SUCCESS)
    * grow filesystem to fill the partition                    (ERROR)
      * btrfs filesystem resize 1:max '/mnt/1'                 (ERROR)
          Resize '/mnt/1' of '1:max'
          ERROR: unable to resize '/mnt/1': Read-only file system

See GitLab issue for the testing results of attempting to online resize
all supporting file system while mounted read-only.  No file system
allows online resizing while mounted read-only, except for reiserfs.
    Issue #10 - Gparted fails to resize btrfs partition that is mounted
    read-only
    #10

Fix by preventing online resizing of *all* file systems mounted
read-only, including reiserfs.  Instead of displaying the resize dialog
in this case, display an information dialog explaining why the partition
can't be resized.  This is similar to what happens when attempting to
create a new partition on a disk without a partition table.  The new
dialog looks like:

    (!) Unable to resize read-only file system /dev/sdb1
        The file system can not be resized while it is mounted read-only.
        Either unmount the file system or remount it read-write.
                                                                   [ OK ]

Closes #10 - Gparted fails to resize btrfs partition that is mounted
             read-only