Fix for this bug can be found at https://codereview.chromium.org/2829993002/

This doesn't deal with overlapping virtual test suites however.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/1a802b27bf4b89e135972cb2e0dbb851524da9ef

commit 1a802b27bf4b89e135972cb2e0dbb851524da9ef
Author: tansell <tansell@chromium.org>
Date: Thu Apr 20 06:45:10 2017

webkit-layout-tests: Revert accidental addition of duplicate virtual tests

The patch "Add wpt/css/CSS2/positioning LayoutNG virtual test suite
(patchset #2 id:20001 of https://codereview.chromium.org/2823223004/ )"
accidentally added the "external/wpt/css/CSS2/abspos" and
"external/wpt/css/CSS2/normal-flow" directory to the virtual suite
twice.

This causes layout tests on swarming to fail because the tests are then
run on two different shards making it impossible to merge the results.

This patch removes the second addition.

TBR=atotic@chromium.org,ikilpatrick@chromium.org,glebl@chromium.org,qyearsley@chromium.org,mcgreevy@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=635619, 713525 

Review-Url: https://codereview.chromium.org/2831053002
Cr-Commit-Position: refs/heads/master@{#465920}

[modify] https://crrev.com/1a802b27bf4b89e135972cb2e0dbb851524da9ef/third_party/WebKit/LayoutTests/VirtualTestSuites

Thanks Tim :-)

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/eaa6185759c3d8f7230851633c724caa73f544e9

commit eaa6185759c3d8f7230851633c724caa73f544e9
Author: tansell <tansell@chromium.org>
Date: Mon Apr 24 04:15:24 2017

webkitpy: Prevent the addition of duplicate virtual tests.

BUG= 713525 

Review-Url: https://codereview.chromium.org/2829993002
Cr-Commit-Position: refs/heads/master@{#466587}

[modify] https://crrev.com/eaa6185759c3d8f7230851633c724caa73f544e9/third_party/WebKit/Tools/Scripts/webkitpy/layout_tests/port/base.py
[modify] https://crrev.com/eaa6185759c3d8f7230851633c724caa73f544e9/third_party/WebKit/Tools/Scripts/webkitpy/layout_tests/port/base_unittest.py