Chrome Version: - 
Chrome OS Version: Version obtained (10/7/18) via these steps:  https://www.chromium.org/chromium-os/quick-start-guide
Chrome OS Platform: KBL PC platform 
Network info: wifi

Please specify Cr-* of the system to which this bug/feature applies (add
the label below).

Steps To Reproduce:
(1) Follow the build steps here: https://www.chromium.org/chromium-os/quick-start-guide
(2) Install onto a blank (fat32 formatted) drive
(3) Install is correct, USB flash drive can boot
(4) Rebuild image
(5) Try to re-install on the same drive (which now has partitions for Chromium)
(6) Install fails
(7) Only solution is to take the USB flash to another PC, and manually delete the partitions and re-format. 

Expected Result:

Expect during install that the USB flash partitions will be deleted, and the drive formatted correctly. 

Actual Result:

Partitions on the USB flash have to be manually deleted, and the flash reformatted. 

How frequently does this problem reproduce? (Always, sometimes, hard to
reproduce?)

Always

What is the impact to the user, and is there a workaround? If so, what is
it?

Poor build experience. Workaround is to delete the partitions/format drive somewhere else.

Please provide any additional information below. Attach a screen shot or
log if possible.

n/a

For graphics-related bugs, please copy/paste the contents of the about:gpu
page at the end of this report.

*Note: this is my first bug submission. If any further details are needed please let me know*