Display the saved file name on quit When a user press 'q' to quit webplot. It clears the canvas and displays the saved filename on the screen. BUG=chromium:443539 TEST=Manually execute webplot.py on a chrome os machine, and press 'q' on chrome to quit. It would clean the canvas and display the saved file on the screen. Change-Id: I9c9d6eb6dc9ce42c48e249c1cb23afbfebeaa99e Reviewed-on: https://chromium-review.googlesource.com/242069 Reviewed-by: Charlie Mooney <[email protected]> Commit-Queue: Shyh-In Hwang <[email protected]> Tested-by: Shyh-In Hwang <[email protected]>