I'd like to deprecate this in July if possible, if there are no more issues that people feel should block this.

I think that now seems like a good time to officially deprecate and turn down rebaseline-o-matic because I believe some (albeit minor) changes are required for it to work with Gerrit. Specifically, it currently assumes we're using Rietveld when getting the CL issue number. Since the change required to switch to Gerrit is small, this is not a hard cut-off.

The real reasons for wanting to deprecate rebaseline-o-matic are:
 - Removing rebaseline-o-matic and `webkit-patch auto-rebaseline` will decrease maintenance burden in the future.
 - Removing these also makes some related bugs (e.g. 693352) obsolete.
 - Making rebaselining from try jobs the normal way of rebaselining has advantages in general.
 - Even if rebaselining from try jobs weren't applicable to all cases, it's still possible to rebaseline from continuous builder results with other webkit-patch rebaseline commands.

I'd like to reference this bug in the deprecation message and message to blink-dev.

Started a CL to add a deprecation warning message at https://chromium-review.googlesource.com/539136.

Update: After removing support for NeedsRebaseline lines, the rebaseline-o-matic bot has now not made any changes for more than two weeks:

https://codereview.chromium.org/search?closed=1&owner=blink-rebaseline-bot%40chromium.org

Next steps:
 1. Remove the rebaseline_o_matic builder from the master config.
 2. Remove the recipe.
 3. Remove the puppet config.
 4. Remove the auto-rebaseline command.

Yay!

Oh, and also: rebaseline-o-matic had its own dedicated slave, vm140-m1, which could be freed up and used for something else.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/tools/build/+/6cd5c61e82b8da7da710e6e01ba0bf500a886f86

commit 6cd5c61e82b8da7da710e6e01ba0bf500a886f86
Author: Quinten Yearsley <qyearsley@google.com>
Date: Thu Jul 06 23:10:17 2017

Remove rebaseline-o-matic from master config in build repo.

Bug:  692811 
Change-Id: Ie76bac627fa83f9c42e024f92d5d85c0cd60bf3d
Reviewed-on: https://chromium-review.googlesource.com/562742
Reviewed-by: Dirk Pranke <dpranke@chromium.org>
Commit-Queue: Quinten Yearsley <qyearsley@chromium.org>

[modify] https://crrev.com/6cd5c61e82b8da7da710e6e01ba0bf500a886f86/masters/master.chromium.infra.cron/slaves.cfg
[modify] https://crrev.com/6cd5c61e82b8da7da710e6e01ba0bf500a886f86/masters/master.chromium.infra.cron/master.cfg

The following revision refers to this bug:
  https://chromium.googlesource.com/infra/infra/+/8c9eb20200b3835a33b4ad91e61527888a547c6b

commit 8c9eb20200b3835a33b4ad91e61527888a547c6b
Author: Quinten Yearsley <qyearsley@google.com>
Date: Mon Jul 10 20:49:27 2017

Remove the rebaseline-o-matic recipe.

This CL would remove the rebaseline-o-matic recipe used by
the rebaseline-o-matic bot. It should only be committed
after the master config is updated[1] and the master is
restarted.

[1] https://chromium-review.googlesource.com/c/562742/

TBR: wkorman
Bug:  692811 
Change-Id: Iaaf7efc45dfca24e9db0e4f357d083bacdff703c
Reviewed-on: https://chromium-review.googlesource.com/562504
Commit-Queue: Quinten Yearsley <qyearsley@chromium.org>
Reviewed-by: Dirk Pranke <dpranke@chromium.org>

[delete] https://crrev.com/5ec2fda564f954f7a5f1e525e4cac0f97be7b610/recipes/recipes/rebaseline_o_matic.expected/rebaseline_o_matic.json
[modify] https://crrev.com/8c9eb20200b3835a33b4ad91e61527888a547c6b/recipes/recipes/OWNERS
[delete] https://crrev.com/5ec2fda564f954f7a5f1e525e4cac0f97be7b610/recipes/recipes/rebaseline_o_matic.py
[delete] https://crrev.com/5ec2fda564f954f7a5f1e525e4cac0f97be7b610/recipes/recipes/rebaseline_o_matic.expected/OWNERS

The following revision refers to this bug:
  https://chrome-internal.googlesource.com/infra/puppet/+/e352f0748db708f2b5777511de4281346f7ea26f

commit e352f0748db708f2b5777511de4281346f7ea26f
Author: Quinten Yearsley <qyearsley@google.com>
Date: Mon Jul 10 21:22:40 2017

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/efac3d1c9b2f05ffe6eeca1b6040d605f792bdaa

commit efac3d1c9b2f05ffe6eeca1b6040d605f792bdaa
Author: Quinten Yearsley <qyearsley@google.com>
Date: Tue Jul 11 00:07:30 2017

Remove auto-rebaseline and the NeedsRebaseline keyword.

Bug:  692811 
Change-Id: Ic1a061020c1dc502655646c7a6e3ae80aee14535
Reviewed-on: https://chromium-review.googlesource.com/564681
Reviewed-by: Dirk Pranke <dpranke@chromium.org>
Commit-Queue: Quinten Yearsley <qyearsley@chromium.org>
Cr-Commit-Position: refs/heads/master@{#485453}
[modify] https://crrev.com/efac3d1c9b2f05ffe6eeca1b6040d605f792bdaa/third_party/WebKit/Tools/Scripts/webkitpy/layout_tests/controllers/manager.py
[modify] https://crrev.com/efac3d1c9b2f05ffe6eeca1b6040d605f792bdaa/third_party/WebKit/Tools/Scripts/webkitpy/layout_tests/lint_test_expectations_unittest.py
[modify] https://crrev.com/efac3d1c9b2f05ffe6eeca1b6040d605f792bdaa/third_party/WebKit/Tools/Scripts/webkitpy/layout_tests/models/test_expectations.py
[modify] https://crrev.com/efac3d1c9b2f05ffe6eeca1b6040d605f792bdaa/third_party/WebKit/Tools/Scripts/webkitpy/layout_tests/models/test_expectations_unittest.py
[modify] https://crrev.com/efac3d1c9b2f05ffe6eeca1b6040d605f792bdaa/third_party/WebKit/Tools/Scripts/webkitpy/layout_tests/models/test_run_results_unittest.py
[modify] https://crrev.com/efac3d1c9b2f05ffe6eeca1b6040d605f792bdaa/third_party/WebKit/Tools/Scripts/webkitpy/layout_tests/port/test.py
[modify] https://crrev.com/efac3d1c9b2f05ffe6eeca1b6040d605f792bdaa/third_party/WebKit/Tools/Scripts/webkitpy/layout_tests/update_flaky_expectations.py
[modify] https://crrev.com/efac3d1c9b2f05ffe6eeca1b6040d605f792bdaa/third_party/WebKit/Tools/Scripts/webkitpy/layout_tests/update_flaky_expectations_unittest.py
[delete] https://crrev.com/5946acdc3a28c62847b18991fe06f86e631a40c1/third_party/WebKit/Tools/Scripts/webkitpy/tool/commands/auto_rebaseline.py
[delete] https://crrev.com/5946acdc3a28c62847b18991fe06f86e631a40c1/third_party/WebKit/Tools/Scripts/webkitpy/tool/commands/auto_rebaseline_unittest.py
[modify] https://crrev.com/efac3d1c9b2f05ffe6eeca1b6040d605f792bdaa/third_party/WebKit/Tools/Scripts/webkitpy/tool/commands/rebaseline.py
[modify] https://crrev.com/efac3d1c9b2f05ffe6eeca1b6040d605f792bdaa/third_party/WebKit/Tools/Scripts/webkitpy/tool/commands/rebaseline_unittest.py
[modify] https://crrev.com/efac3d1c9b2f05ffe6eeca1b6040d605f792bdaa/third_party/WebKit/Tools/Scripts/webkitpy/tool/webkit_patch.py

Alright, I think everything that I planned to do here is now done.

There's one more comment somewhere that refers to rebaseline-o-matic; I'll be sure to remove that later.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/d13299d0d6508ca8c1a53fb9ec1eac5a000d7064

commit d13299d0d6508ca8c1a53fb9ec1eac5a000d7064
Author: Quinten Yearsley <qyearsley@google.com>
Date: Tue Jul 25 17:22:17 2017

Update layout test rebaselining documentation

This removes mention of NeedsRebaseline/rebaseline-o-matic, which have
now been removed.

Bug:  692811 
Change-Id: I9893eef07c7380186398a89a7cfdbcd524627193
Reviewed-on: https://chromium-review.googlesource.com/584941
Reviewed-by: Jeff Carpenter <jeffcarp@chromium.org>
Commit-Queue: Quinten Yearsley <qyearsley@chromium.org>
Cr-Commit-Position: refs/heads/master@{#489350}
[modify] https://crrev.com/d13299d0d6508ca8c1a53fb9ec1eac5a000d7064/docs/testing/layout_test_expectations.md