The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/4c59a1b8d24fb92f8acac25baed78cf6155f647c

commit 4c59a1b8d24fb92f8acac25baed78cf6155f647c
Author: yamaguchi <yamaguchi@chromium.org>
Date: Wed Oct 26 07:59:49 2016

Suppress warnings on unplugging read-only removable devices.

BUG= 653820 
TEST=Manual test on a device by plugging & unplugging a write-protected SD card.

Review-Url: https://codereview.chromium.org/2445193004
Cr-Commit-Position: refs/heads/master@{#427631}

[modify] https://crrev.com/4c59a1b8d24fb92f8acac25baed78cf6155f647c/chrome/browser/chromeos/extensions/file_manager/device_event_router.cc
[modify] https://crrev.com/4c59a1b8d24fb92f8acac25baed78cf6155f647c/chrome/browser/chromeos/extensions/file_manager/device_event_router_unittest.cc

I'd like to merge the commit (comment #2) to M55 as a part of the fix for https://code.google.com/p/chrome-os-partner/issues/detail?id=58309.

Your change meets the bar and is auto-approved for M55 (branch: 2883)

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/c441c4caea7e1aabcfd31aed56c091486a4e9af0

commit c441c4caea7e1aabcfd31aed56c091486a4e9af0
Author: Naoki Fukino <fukino@chromium.org>
Date: Wed Nov 02 04:36:45 2016

Suppress warnings on unplugging read-only removable devices.

BUG= 653820 
TEST=Manual test on a device by plugging & unplugging a write-protected SD card.
TBR=yamaguchi@chromium.org

Review-Url: https://codereview.chromium.org/2445193004
Cr-Commit-Position: refs/heads/master@{#427631}
(cherry picked from commit 4c59a1b8d24fb92f8acac25baed78cf6155f647c)

Review URL: https://codereview.chromium.org/2472643002 .

Cr-Commit-Position: refs/branch-heads/2883@{#417}
Cr-Branched-From: 614d31daee2f61b0180df403a8ad43f20b9f6dd7-refs/heads/master@{#423768}

[modify] https://crrev.com/c441c4caea7e1aabcfd31aed56c091486a4e9af0/chrome/browser/chromeos/extensions/file_manager/device_event_router.cc
[modify] https://crrev.com/c441c4caea7e1aabcfd31aed56c091486a4e9af0/chrome/browser/chromeos/extensions/file_manager/device_event_router_unittest.cc

Still seeing warning with write protected SD cards on 

55.0.2883.42/8872.44.0 cyan

Confirmed on 55.0.2883.42/8872.44.0 cyan that hard-unplugged notification is still seen.
55.0.2883.42/8872.44.0 includes the patch of Comment 8, so it is weird.
Pushing the latest chrome to platform 8872.44.0 fixes the issue.

yamaguchi@, is there any depended CL (in Chrome side) to detect the write-protected SD card as read only?

BTW, I confirmed that removing the USB-C dock from 55.0.2883.42/8872.44.0 chell does not show the hard-unplugged notification.
So the issue reported in comment #9 does not block issue chrome-os-partner:58309.

I checked with 55.0.2883.42 (8872.44.0)
With cyan device, I could reproduce the issue with a bit modified repro steps:

1. Sign in as Guest, by "Browse as Guest" button.
2. Plug a write-protected SD card.  [at this point, it is mounted in RO mode]
3. Unplug the SD card.  [does not show warning]
4. Plug the SD card again.   [it shows up as read-write device in Files app.]
5. Unplug the SD card.  [shows the warning]
6. (repeat 4--5)

With link device, the issue did not reproduce.

So far we saw that the issue doesn't reproduce anymore with cyan + M56 (trunk).
Since this didn't reproduce in link, it looks like a new bug rather than just missing cherrypick of some dependency change.

I think showing notification for read-only device is not a regression,
but recognizing read-only device as read-write device may be a regression (unless the bug hadn't been fixed in cyan + M54).
https://bugs.chromium.org/p/chromium/issues/detail?id=644077

Should this issue be marked as Fixed as the issue is no longer reproducible?

Yes, this issues reproduces with the combination of cyan + M55, but going to be fixed in M56.
Feel free to reopen if supporting this feature on cyan M55 is considered more important.

Issue still exists in M55 but fixed in M56. 

Tested on 56.0.2924.17/9000.18.0