This is interesting - we don't do any different calls on CrOS vs other platforms from the extensions API, where we just call SelectFileDialog methods.  I wonder if it's something in there?  (especially if it's a regression)

Oh dear, this doesn't look good. Thanks for filing.

noel - can you PTAL?

This caused DCHECKs to fail on CrOS builds for me. Root cause was existing code using "default" clauses in "switch (type)" statements, which prevented the compiler from catching the missing impl. I took a quick look, and the fix seemed obvious/simple, and chrome:://extensions folder picker now works for me. Up for review: https://chromium-review.googlesource.com/#/c/chromium/src/+/1089877

 Issue 849775  has been merged into this issue.

Given that  issue 849775  was merged here, updating labels and RBS status.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/eb43c62a34f5b7335a846d579143f8cc4cc777a8

commit eb43c62a34f5b7335a846d579143f8cc4cc777a8
Author: Yuri Wiitala <miu@chromium.org>
Date: Thu Jun 07 20:45:00 2018

CrOS: Fix DCHECK failures in SelectFileDialog.

Commit cc859bf07d39ffb99f1e19827c894327fb4d9849 introduced a new variant
of select file dialog: SELECT_EXISTING_FOLDER. Because existing code
used 'default' clauses in multiple switch statements, the compiler did
not catch that there was missing impl for the ChromeOS UI. This change
adds that missing impl.

Bug:  772180 , 848303 
Change-Id: Ic990bf838d3a8c300414259f246715ae2efdcfe3
Reviewed-on: https://chromium-review.googlesource.com/1089877
Reviewed-by: Thomas Anderson <thomasanderson@chromium.org>
Reviewed-by: Noel Gordon <noel@chromium.org>
Commit-Queue: Yuri Wiitala <miu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#565396}
[modify] https://crrev.com/eb43c62a34f5b7335a846d579143f8cc4cc777a8/chrome/browser/chromeos/file_manager/select_file_dialog_util.cc
[modify] https://crrev.com/eb43c62a34f5b7335a846d579143f8cc4cc777a8/chrome/browser/chromeos/file_manager/url_util.cc
[modify] https://crrev.com/eb43c62a34f5b7335a846d579143f8cc4cc777a8/chrome/browser/ui/libgtkui/select_file_dialog_impl_gtk.cc
[modify] https://crrev.com/eb43c62a34f5b7335a846d579143f8cc4cc777a8/chrome/browser/ui/libgtkui/select_file_dialog_impl_kde.cc

Fixed. Requesting M68 merge.

This bug requires manual review: M68 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), kariahda@(iOS), bhthompson@(ChromeOS), abdulsyed@(Desktop)

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

This issue has been approved for a merge. Please merge the fix to any appropriate branches as soon as possible!

If all merges have been completed, please remove any remaining Merge-Approved labels from this issue.

Thanks for your time! To disable nags, add the Disable-Nags label.

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

@miu: Merge has been approved. Can you post a status update on merging to M68?

Just got back from vacation today. Will land today.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/dac5bc2969e50cc116d11eccca55f2bb216b9af5

commit dac5bc2969e50cc116d11eccca55f2bb216b9af5
Author: Yuri Wiitala <miu@chromium.org>
Date: Mon Jun 18 21:27:37 2018

CrOS: Fix DCHECK failures in SelectFileDialog.

Commit cc859bf07d39ffb99f1e19827c894327fb4d9849 introduced a new variant
of select file dialog: SELECT_EXISTING_FOLDER. Because existing code
used 'default' clauses in multiple switch statements, the compiler did
not catch that there was missing impl for the ChromeOS UI. This change
adds that missing impl.

Bug:  772180 , 848303 
Change-Id: Ic990bf838d3a8c300414259f246715ae2efdcfe3
Reviewed-on: https://chromium-review.googlesource.com/1089877
Reviewed-by: Thomas Anderson <thomasanderson@chromium.org>
Reviewed-by: Noel Gordon <noel@chromium.org>
Commit-Queue: Yuri Wiitala <miu@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#565396}(cherry picked from commit eb43c62a34f5b7335a846d579143f8cc4cc777a8)
Reviewed-on: https://chromium-review.googlesource.com/1105237
Reviewed-by: Yuri Wiitala <miu@chromium.org>
Cr-Commit-Position: refs/branch-heads/3440@{#421}
Cr-Branched-From: 010ddcfda246975d194964ccf20038ebbdec6084-refs/heads/master@{#561733}
[modify] https://crrev.com/dac5bc2969e50cc116d11eccca55f2bb216b9af5/chrome/browser/chromeos/file_manager/select_file_dialog_util.cc
[modify] https://crrev.com/dac5bc2969e50cc116d11eccca55f2bb216b9af5/chrome/browser/chromeos/file_manager/url_util.cc
[modify] https://crrev.com/dac5bc2969e50cc116d11eccca55f2bb216b9af5/chrome/browser/ui/libgtkui/select_file_dialog_impl_gtk.cc
[modify] https://crrev.com/dac5bc2969e50cc116d11eccca55f2bb216b9af5/chrome/browser/ui/libgtkui/select_file_dialog_impl_kde.cc

I've merged to refs/branch-heads/3440. Will ChromeOS release builds pick this up automatically, or do I need to cherry-pick into other branches?

Looking at the ChromeOS M68 branch instructions, it includes Chrome Branch: 3440, so I don't think you need to cherry-pick to any other branches.

Adding Steven to verify.

you should be fine - release builder will pick up changes on the Chrome branch (well, they already have for in this case)