How to do this: 
1) Pick a test
2) convert it to wpt format if it is not already in that format
3) Remove chrome specific hacks
4) Move to the new location and ask for a blink review :)
5) :)

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/d2402dd2fa530657f0be36f6cc74d41f71d894e6

commit d2402dd2fa530657f0be36f6cc74d41f71d894e6
Author: Yi Gu <yigu@chromium.org>
Date: Thu Jan 10 17:46:44 2019

[Animation Worklet] Upstream worklet animation with fill mode test to WPT

This CL upstreams worklet animation with fill mode test to WPT. There is
no behavior change to the test.
It also adds common.js which contains necessary helper APIs.

Bug: 915352
Change-Id: I6d045891385a59fad19e6edeb15ce47809ae26bd
Reviewed-on: https://chromium-review.googlesource.com/c/1404749
Reviewed-by: Stephen McGruer <smcgruer@chromium.org>
Commit-Queue: Yi Gu <yigu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#621627}
[add] https://crrev.com/d2402dd2fa530657f0be36f6cc74d41f71d894e6/third_party/blink/web_tests/external/wpt/animation-worklet/common.js
[rename] https://crrev.com/d2402dd2fa530657f0be36f6cc74d41f71d894e6/third_party/blink/web_tests/external/wpt/animation-worklet/worklet-animation-with-fill-mode.https.html

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/2e2ded718a780daf22373b1a2b53bdf35106f80c

commit 2e2ded718a780daf22373b1a2b53bdf35106f80c
Author: Yi Gu <yigu@chromium.org>
Date: Thu Jan 10 18:00:40 2019

[Animation Worklet] Upstream worklet animation with invalid effect test to WPT

This CL upstreams worklet animation with invalid effect test to WPT and
adds necessary API to the helper file. There is no behavior change to
the test.

Bug: 915352
Change-Id: I59af33fe7cf6ec390c06f13c5c884a1ba4fbb078
Reviewed-on: https://chromium-review.googlesource.com/c/1405288
Commit-Queue: Yi Gu <yigu@chromium.org>
Reviewed-by: Xida Chen <xidachen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#621632}
[delete] https://crrev.com/e20729b1c9ecb4d873a2c89b56b378cb369eb50f/third_party/blink/web_tests/animations/animationworklet/worklet-animation-with-invalid-effect.html
[modify] https://crrev.com/2e2ded718a780daf22373b1a2b53bdf35106f80c/third_party/blink/web_tests/external/wpt/animation-worklet/common.js
[add] https://crrev.com/2e2ded718a780daf22373b1a2b53bdf35106f80c/third_party/blink/web_tests/external/wpt/animation-worklet/worklet-animation-with-invalid-effect.https.html

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/9afafd8fa37175cd36bf01c8f272c39a75d2e1f8

commit 9afafd8fa37175cd36bf01c8f272c39a75d2e1f8
Author: Yi Gu <yigu@chromium.org>
Date: Thu Jan 10 19:23:13 2019

[Animation Worklet] Upstream scroll timeline writing modes test to WPT

This CL upstreams scroll timeline writing modes test to WPT. There is no
behavior change to the test.

Bug: 915352
Change-Id: Ibc0e078fb2b547b82d57df30b57535d392d85535
Reviewed-on: https://chromium-review.googlesource.com/c/1405438
Reviewed-by: Xida Chen <xidachen@chromium.org>
Commit-Queue: Yi Gu <yigu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#621698}
[rename] https://crrev.com/9afafd8fa37175cd36bf01c8f272c39a75d2e1f8/third_party/blink/web_tests/external/wpt/animation-worklet/scroll-timeline-writing-modes.https.html

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/08959ab16e7dbed8f6472d989420a1a5cfb59b01

commit 08959ab16e7dbed8f6472d989420a1a5cfb59b01
Author: Yi Gu <yigu@chromium.org>
Date: Thu Jan 10 20:03:30 2019

[Animation Worklet] Upstream animation worklet inside iframe test to WPT

This CL upstreams animation worklet inside iframe test to WPT. There is
no behavior change to the test.

Bug: 915352
Change-Id: I2fdc46471014286a81623020eb560e29afac2dd8
Reviewed-on: https://chromium-review.googlesource.com/c/1405489
Commit-Queue: Yi Gu <yigu@chromium.org>
Reviewed-by: Stephen McGruer <smcgruer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#621721}
[rename] https://crrev.com/08959ab16e7dbed8f6472d989420a1a5cfb59b01/third_party/blink/web_tests/external/wpt/animation-worklet/animation-worklet-inside-iframe.https.html
[rename] https://crrev.com/08959ab16e7dbed8f6472d989420a1a5cfb59b01/third_party/blink/web_tests/external/wpt/animation-worklet/resources/animator-iframe.html

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/85c4dcec46ee24b011320781e22180e57513816e

commit 85c4dcec46ee24b011320781e22180e57513816e
Author: Majid Valipour <majidvp@chromium.org>
Date: Thu Jan 17 21:05:11 2019

[animation-worklet] Enable wpt tests to run with threaded compostiting


Bug: 915352
Change-Id: Iead91d55465c0277dfaa9588d413e654a5d1a57a
Reviewed-on: https://chromium-review.googlesource.com/c/1418076
Commit-Queue: Majid Valipour <majidvp@chromium.org>
Reviewed-by: Xida Chen <xidachen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#623836}
[modify] https://crrev.com/85c4dcec46ee24b011320781e22180e57513816e/third_party/blink/web_tests/VirtualTestSuites
[add] https://crrev.com/85c4dcec46ee24b011320781e22180e57513816e/third_party/blink/web_tests/virtual/threaded/external/wpt/animation-worklet/README.txt

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/77aa48f116cb547c0abb7ce4f37293b006c23d99

commit 77aa48f116cb547c0abb7ce4f37293b006c23d99
Author: Majid Valipour <majidvp@chromium.org>
Date: Thu Jan 17 22:44:19 2019

[animation-worklet] clean up wpt tests

- Fix a test that should have been an async test but was not.
- Use existing web-animation common utils where applicable.
- Introduce and use common worklets (passthrough, constant_time) for testing.


Bug: 915352
Change-Id: I5f503bebe3bc4be4f3c76a84604df63a905439e2
Reviewed-on: https://chromium-review.googlesource.com/c/1409807
Reviewed-by: Yi Gu <yigu@chromium.org>
Commit-Queue: Majid Valipour <majidvp@chromium.org>
Cr-Commit-Position: refs/heads/master@{#623880}
[modify] https://crrev.com/77aa48f116cb547c0abb7ce4f37293b006c23d99/third_party/blink/web_tests/external/wpt/animation-worklet/animation-worklet-inside-iframe.https.html
[modify] https://crrev.com/77aa48f116cb547c0abb7ce4f37293b006c23d99/third_party/blink/web_tests/external/wpt/animation-worklet/common.js
[modify] https://crrev.com/77aa48f116cb547c0abb7ce4f37293b006c23d99/third_party/blink/web_tests/external/wpt/animation-worklet/resources/animator-iframe.html
[modify] https://crrev.com/77aa48f116cb547c0abb7ce4f37293b006c23d99/third_party/blink/web_tests/external/wpt/animation-worklet/scroll-timeline-writing-modes.https.html
[modify] https://crrev.com/77aa48f116cb547c0abb7ce4f37293b006c23d99/third_party/blink/web_tests/external/wpt/animation-worklet/worklet-animation-with-fill-mode.https.html
[modify] https://crrev.com/77aa48f116cb547c0abb7ce4f37293b006c23d99/third_party/blink/web_tests/external/wpt/animation-worklet/worklet-animation-with-invalid-effect.https.html

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/de19f338aa8fc7e4e99d5b07a1b154923b6f0217

commit de19f338aa8fc7e4e99d5b07a1b154923b6f0217
Author: Findit <findit-for-me@appspot.gserviceaccount.com>
Date: Fri Jan 18 03:18:31 2019

Revert "[animation-worklet] Enable wpt tests to run with threaded compostiting"

This reverts commit 85c4dcec46ee24b011320781e22180e57513816e.

Reason for revert:

Findit (https://goo.gl/kROfz5) identified CL at revision 623836 as the
culprit for flakes in the build cycles as shown on:
https://findit-for-me.appspot.com/waterfall/flake/flake-culprit?key=ag9zfmZpbmRpdC1mb3ItbWVyQwsSDEZsYWtlQ3VscHJpdCIxY2hyb21pdW0vODVjNGRjZWM0NmVlMjRiMDExMzIwNzgxZTIyMTgwZTU3NTEzODE2ZQw

Sample Failed Build: https://ci.chromium.org/buildbot/chromium.mac/Mac10.11%20Tests/33028

Sample Failed Step: webkit_layout_tests on (none) GPU on Mac on Mac-10.11.6

Sample Flaky Test: virtual/threaded/external/wpt/animation-worklet/current-time.https.html

Original change's description:
> [animation-worklet] Enable wpt tests to run with threaded compostiting
> 
> 
> Bug: 915352
> Change-Id: Iead91d55465c0277dfaa9588d413e654a5d1a57a
> Reviewed-on: https://chromium-review.googlesource.com/c/1418076
> Commit-Queue: Majid Valipour <majidvp@chromium.org>
> Reviewed-by: Xida Chen <xidachen@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#623836}

Change-Id: I2eb82ad256d0ec8f370b8d160b4a150933196623
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 915352,  923225 
Reviewed-on: https://chromium-review.googlesource.com/c/1420303
Cr-Commit-Position: refs/heads/master@{#623987}
[modify] https://crrev.com/de19f338aa8fc7e4e99d5b07a1b154923b6f0217/third_party/blink/web_tests/VirtualTestSuites
[delete] https://crrev.com/a5e641f741c98c4ee25ebb8f9105398f7cad2d81/third_party/blink/web_tests/virtual/threaded/external/wpt/animation-worklet/README.txt