This seems rare, since it's a combination of switching between touch/keyboard and using keyboard shortcuts. It's also easily fixable by tapping inside the input, though holding the backspace button on the PIN pad also lets you delete the entered text.

Moving to P3, not a launch blocker.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/344b6d2380dbbf312a4725c308eb0cd4d0627177

commit 344b6d2380dbbf312a4725c308eb0cd4d0627177
Author: sammiequon <sammiequon@chromium.org>
Date: Sat Nov 12 04:37:45 2016

cros: Allow pin keyboard to keep focus without popping up the pin keyboard.

We want each button click to transfer focus back to the pin keyboard, but this not work well with virtual keyboard. Previously kept focus on the buttons, but added key events to each button so they users can still use the keyboard after pressing a keyboard. This CL tries another method by preventing the virtual keyboard from popping up on button clicks. Since I was working on the PIN, I changed the input back to type text which fixes the bug with the caret jumping around when non-numerical input is entered.

BUG= 653297 ,  653642 ,  661334 
TEST=none
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:closure_compilation

Review-Url: https://codereview.chromium.org/2444443002
Cr-Commit-Position: refs/heads/master@{#431769}

[modify] https://crrev.com/344b6d2380dbbf312a4725c308eb0cd4d0627177/chrome/browser/resources/chromeos/quick_unlock/pin_keyboard.html
[modify] https://crrev.com/344b6d2380dbbf312a4725c308eb0cd4d0627177/chrome/browser/resources/chromeos/quick_unlock/pin_keyboard.js
[modify] https://crrev.com/344b6d2380dbbf312a4725c308eb0cd4d0627177/chrome/browser/ui/webui/chromeos/login/core_oobe_handler.cc
[modify] https://crrev.com/344b6d2380dbbf312a4725c308eb0cd4d0627177/chrome/browser/ui/webui/chromeos/login/core_oobe_handler.h
[modify] https://crrev.com/344b6d2380dbbf312a4725c308eb0cd4d0627177/ui/keyboard/BUILD.gn
[modify] https://crrev.com/344b6d2380dbbf312a4725c308eb0cd4d0627177/ui/keyboard/keyboard_util.cc
[add] https://crrev.com/344b6d2380dbbf312a4725c308eb0cd4d0627177/ui/keyboard/scoped_keyboard_disabler.cc
[add] https://crrev.com/344b6d2380dbbf312a4725c308eb0cd4d0627177/ui/keyboard/scoped_keyboard_disabler.h
[modify] https://crrev.com/344b6d2380dbbf312a4725c308eb0cd4d0627177/ui/login/account_picker/user_pod_row.js

Verified on ChromeOS 9000.8.0, 56.0.2924.7