This is blocking csswg-test import, so I want to solve it soon.

The easiest and least controversial fix would probably be to add a step in the import process that checks for CRLF endings, spits out a warning, then converts the file to use LF line endings.

 Issue 662667  has been merged into this issue.

Update: Looking back, I did already decide earlier that excluding imported files from Chromium presubmit checks is probably reasonable: https://codereview.chromium.org/2374203003, and also when uploading CLs, the w3c-test-importer calls "git cl upload -f", which I would expect should mean "ignore presubmit warnings, only abort on presubmit errors".

The CRLF line ending presubmit check is still run because the black-list at the top of src/PRESUBMIT.py is not used when running some checks (including the CRLF check), and the upload still fails despite -f because it turns out that -f actually means "don't prompt, just fail", rather than "don't prompt and pass if there are just warnings" (https://cs.chromium.org/chromium/tools/depot_tools/presubmit_support.py?l=1281).

So:

 - If the -f flag was intended to mean "ignore warnings, force upload", then that should be changed.
 - If the black list at the top of src/PRESUBMIT.py was intended to apply to all of the checks, then that should be changed.

If either one of those changes are made, then w3c-test-importer should ignore CRLF line endings when importing tests, I believe.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/tools/depot_tools.git/+/516fe7f8818dd27a9a2161a79492371712e06849

commit 516fe7f8818dd27a9a2161a79492371712e06849
Author: Quinten Yearsley <qyearsley@google.com>
Date: Wed Dec 14 19:50:18 2016

Presubmit: if there are warnings and may_prompt is false, don't fail.

Rationale: The description of the -f flag to git cl upload is "force
yes to questions (don't prompt)", so when git cl upload -f is run,
I would expect it to abort on errors, but still continue on warnings.

When the -f is given, DoPresubmitChecks is called with may_prompt=False;
this CL would change the behavior of DoPresubmitChecks so that when
may_prompt is False and there are warnings but no errors, then that
means we will print warnings but not fail.

BUG= 671683 

Change-Id: Ie0f1ac1983d875226db8ad741cbce3dc0bc4eb96
Reviewed-on: https://chromium-review.googlesource.com/419148
Reviewed-by: Aaron Gable <agable@chromium.org>
Commit-Queue: Quinten Yearsley <qyearsley@chromium.org>

[modify] https://crrev.com/516fe7f8818dd27a9a2161a79492371712e06849/presubmit_support.py
[modify] https://crrev.com/516fe7f8818dd27a9a2161a79492371712e06849/tests/presubmit_unittest.py

After the above change, the CSS changes are now being uploaded, but still not being committed -- they're failing in the chromium_presubmit try bot. The same presubmit warning is happening there, but is a fatal error there.

Example CSS import CL:
https://codereview.chromium.org/2593703002

One possible next step. Change top-level PRESUBMIT.py so that some checks *actually* aren't done for //third_party/WebKit. (Pan-project checks aren't done since this directory is in _EXCLUDED_PATHS, but _EXCLUDED_PATHS isn't used for all checks.)

Update: I made a CL https://codereview.chromium.org/2598743002 to convert line endings upon import, but then gsnedders@ noted that there's already a lint check upstream for line endings, so we're expecting this not to be an issue in the future, so once it's fixed upstream then this should be fixed.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/tools/depot_tools.git/+/e9c794ea4e4d1c62729757ed20c3dffb5a877914

commit e9c794ea4e4d1c62729757ed20c3dffb5a877914
Author: Quinten Yearsley <qyearsley@google.com>
Date: Mon Dec 19 18:35:32 2016

Make DoPresubmitChecks unit tests clearer.

This is a follow-up to https://chromium-review.googlesource.com/c/419148/;
the purpose is to confirm that the behavior is how we want it to be when
there are presubmit errors and warnings.

BUG= 671683 

Change-Id: I5b295c200d3db1a374e4294bdd78a777ae36c832
Reviewed-on: https://chromium-review.googlesource.com/420975
Commit-Queue: Quinten Yearsley <qyearsley@chromium.org>
Reviewed-by: Dirk Pranke <dpranke@chromium.org>
Reviewed-by: Aaron Gable <agable@chromium.org>

[modify] https://crrev.com/e9c794ea4e4d1c62729757ed20c3dffb5a877914/tests/presubmit_unittest.py

I made a change upstream to remove the CRLF endings, so this is no longer an immediate issue.

I don't believe that this is an issue now (since I believe that the importer ignores presubmit warnings, and only halts on presubmit errors). Will re-open if this is actually an issue still.