Removing iOS label since this doesn't look like an iOS issue.

yamaguchi@ - Could you please take a look?

Have a reproduction now.

https://chromium-review.googlesource.com/c/chromium/src/+/1018624
"Currently Zip Archiver run in the normal and incognito contexts in
parallel when opening a single ZIP file in the Files app.
The instance in the incognito context also receives and process event in
onGetMetadataRequested, but it always fails because it doesn't run the
normal initialization procedure.
(i.e. loading volume and filling unpacker.app.volumeLoadedPromises)"

Both instance registers its callback like:
> chrome.fileSystemProvider.onGetMetadataRequested.addListener(
>    unpacker.app.onGetMetadataRequested);
So it seems these are receiving all events regardless which file it is.
Is this intended behavior of FileSystemProvider API?
(if so, should each extension ignore GetMetadataRequested events when it doesn't know about the file?)

The "error" is handled here.
https://cs.chromium.org/chromium/src/chrome/browser/resources/chromeos/zip_archiver/js/app.js?q=ensurevolumeloaded_&sq=package:chromium&l=274&rcl=6c5d3313ebb5a367620458189b41c9663cb730c4
The case of "did not mount the file but received read request for it" was assumed to happen only when resuming mount status at startup. Now we found it can also happen with this case.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/430b4497a96dfc6e706f9387a559ed0be1d35967

commit 430b4497a96dfc6e706f9387a559ed0be1d35967
Author: Tatsuhisa Yamaguchi <yamaguchi@google.com>
Date: Thu Apr 26 08:14:11 2018

Zip Archiver: Suppress in incognito context of regular session.

Currently Zip Archiver run in the normal and incognito contexts in
parallel when opening a single ZIP file in the Files app.
The instance in the incognito context also received and processed events
in onGetMetadataRequested, but it always fails because it doesn't run
the normal initialization procedure.
(i.e. loading volume and filling unpacker.app.volumeLoadedPromises)

It once had worked harmlessly because error was ignored, but now
the error in the incognito context triggers unmounting of the file.
It can cancel out the volume mounted by the other instance in the
normal context right before it.

Bug:  833603 
Cq-Include-Trybots: master.tryserver.chromium.linux:closure_compilation
Change-Id: I712a974ca4fe287d795256fc22a62d5c85d66401
Reviewed-on: https://chromium-review.googlesource.com/1018624
Commit-Queue: Tatsuhisa Yamaguchi <yamaguchi@chromium.org>
Reviewed-by: Yuki Awano <yawano@chromium.org>
Cr-Commit-Position: refs/heads/master@{#553950}
[modify] https://crrev.com/430b4497a96dfc6e706f9387a559ed0be1d35967/chrome/browser/resources/chromeos/zip_archiver/js/background.js

Hi there, this isn't a M67 regression (discovered in M66).   Also unclear if the change has been tested to ensure no further impact.

This has regressed on M66 and we would like to fix it in M67 considering its importance.
We've discovered  Issue 837251  and the fix will also be in soon.

kbleicher@ - Just to add, as an M66 regression, we probably should have resolved for M66, but given the current timelines M67 is the soonest we can get this fix in.

This bug requires manual review: M67 has already been promoted to the beta branch, so this requires manual review
Please contact the milestone owner if you have questions.
Owners: cmasso@(Android), cmasso@(iOS), kbleicher@(ChromeOS), govind@(Desktop)

For more details visit https://www.chromium.org/issue-tracking/autotriage - Your friendly Sheriffbot

Thanks for the updates.  Can you comment on testing? Don't see that answered....  Need to make sure this doesn't result in unanticipated results.

Seems the fix is initially landed in 68.0.3410.0(comment#9).  I'll check the issue once the build is available. 

Verified the fix on 68.0.3416.0/10635.0.0 (Canary)- Candy.  

Approving merge to M67 Chrome OS. 

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/fdffaeea581913b29a4c69a4d0939a22cc848226

commit fdffaeea581913b29a4c69a4d0939a22cc848226
Author: Tatsuhisa Yamaguchi <yamaguchi@google.com>
Date: Wed May 02 01:12:46 2018

Zip Archiver: Suppress in incognito context of regular session.

Currently Zip Archiver run in the normal and incognito contexts in
parallel when opening a single ZIP file in the Files app.
The instance in the incognito context also received and processed events
in onGetMetadataRequested, but it always fails because it doesn't run
the normal initialization procedure.
(i.e. loading volume and filling unpacker.app.volumeLoadedPromises)

It once had worked harmlessly because error was ignored, but now
the error in the incognito context triggers unmounting of the file.
It can cancel out the volume mounted by the other instance in the
normal context right before it.

Bug:  833603 
Cq-Include-Trybots: master.tryserver.chromium.linux:closure_compilation
Change-Id: I712a974ca4fe287d795256fc22a62d5c85d66401
Reviewed-on: https://chromium-review.googlesource.com/1018624
Commit-Queue: Tatsuhisa Yamaguchi <yamaguchi@chromium.org>
Reviewed-by: Yuki Awano <yawano@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#553950}(cherry picked from commit 430b4497a96dfc6e706f9387a559ed0be1d35967)
Reviewed-on: https://chromium-review.googlesource.com/1038767
Reviewed-by: Tatsuhisa Yamaguchi <yamaguchi@chromium.org>
Cr-Commit-Position: refs/branch-heads/3396@{#434}
Cr-Branched-From: 9ef2aa869bc7bc0c089e255d698cca6e47d6b038-refs/heads/master@{#550428}
[modify] https://crrev.com/fdffaeea581913b29a4c69a4d0939a22cc848226/chrome/browser/resources/chromeos/zip_archiver/js/background.js

Verified the fix in Chrome 67.0.3396.41/ CrOS 10575.32.0 - Peppy, Paine, Mickey

Issue 854436 has been merged into this issue.