Related spec issue: https://github.com/w3c/css-houdini-drafts/issues/410

This is blocked by the spec discussion.

[Status Update]
According to the spec discussion, "CSS" will be changed from "interface" to "namespace". "namespace" is not supported yet in Blink and the blink-bindings team is now planning to work on "namespace" support ( issue 719303 ).

As a stopgap, I'm making "paintWorklet" static attribute to simulate an attribute-on-namespace and moving it to "CSS" interface:
(WIP CL) https://codereview.chromium.org/2896773002/

Hmm... this could be blocked by a V8 bug. See this for details:
https://codereview.chromium.org/2896773002/#msg35

I've confirmed that http/tests/worklet/chromium/import-on-detached-iframe.html in https://codereview.chromium.org/2896773002/ passes with applying https://codereview.chromium.org/2770003002/ .

Good to know. Thank you for confirming it. Do you think it would be possible to land it soon?

Re c#10, I just saw this comment :) https://bugs.chromium.org/p/v8/issues/detail?id=6156#c3

Yeah, I think it's not easy, but let's try our best.  Let's continue the discussion at https://bugs.chromium.org/p/v8/issues/detail?id=6156 .

This is still blocked by static attribute / namespace issues.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/bc9dd77abc396e48a6de5b0b1ea9a34c6953cb5a

commit bc9dd77abc396e48a6de5b0b1ea9a34c6953cb5a
Author: Hiroki Nakagawa <nhiroki@chromium.org>
Date: Fri Aug 25 04:03:51 2017

PaintWorklet: Move paintWorklet from "window" to "CSS"

Before this CL, "paintWorklet" attribute is defined on "Window" interface, but
that should be defined on "CSS" interface[1].

According to the spec discussion[2], "CSS" will be changed from "interface" to
"namespace", but "namespace" is not supported yet in Blink. As a stopgap, this
CL changes "paintWorklet" to a static attribute and moves it to "CSS" interface
to emulate an attribute-on-namespace.

[1] https://drafts.css-houdini.org/css-paint-api-1/#dom-css-paintworklet
[2] https://github.com/w3c/css-houdini-drafts/issues/410

Bug:  719303 
Change-Id: I01f371f0d4f9a193352d1ede1fe28632d52cf312
Reviewed-on: https://chromium-review.googlesource.com/630899
Commit-Queue: Hiroki Nakagawa <nhiroki@chromium.org>
Reviewed-by: Yuki Shiino <yukishiino@chromium.org>
Reviewed-by: Xida Chen <xidachen@chromium.org>
Reviewed-by: Ian Kilpatrick <ikilpatrick@chromium.org>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Cr-Commit-Position: refs/heads/master@{#497319}
[modify] https://crrev.com/bc9dd77abc396e48a6de5b0b1ea9a34c6953cb5a/third_party/WebKit/LayoutTests/external/wpt/common/css-paint-tests.js
[modify] https://crrev.com/bc9dd77abc396e48a6de5b0b1ea9a34c6953cb5a/third_party/WebKit/LayoutTests/external/wpt/css-paint-api/valid-image-after-load.html
[modify] https://crrev.com/bc9dd77abc396e48a6de5b0b1ea9a34c6953cb5a/third_party/WebKit/LayoutTests/external/wpt/css-paint-api/valid-image-before-load.html
[modify] https://crrev.com/bc9dd77abc396e48a6de5b0b1ea9a34c6953cb5a/third_party/WebKit/LayoutTests/http/tests/csspaint/resources/test-runner-invalidation-logging.js
[modify] https://crrev.com/bc9dd77abc396e48a6de5b0b1ea9a34c6953cb5a/third_party/WebKit/LayoutTests/http/tests/csspaint/resources/test-runner-paint-worklet.js
[modify] https://crrev.com/bc9dd77abc396e48a6de5b0b1ea9a34c6953cb5a/third_party/WebKit/LayoutTests/http/tests/devtools/console/console-on-paint-worklet.html
[modify] https://crrev.com/bc9dd77abc396e48a6de5b0b1ea9a34c6953cb5a/third_party/WebKit/LayoutTests/http/tests/devtools/console/paintworklet-console-selector.html
[modify] https://crrev.com/bc9dd77abc396e48a6de5b0b1ea9a34c6953cb5a/third_party/WebKit/LayoutTests/http/tests/security/contentSecurityPolicy/worklet-import-blocked.html
[modify] https://crrev.com/bc9dd77abc396e48a6de5b0b1ea9a34c6953cb5a/third_party/WebKit/LayoutTests/http/tests/worklet/chromium/import-filesystem-url.html
[modify] https://crrev.com/bc9dd77abc396e48a6de5b0b1ea9a34c6953cb5a/third_party/WebKit/LayoutTests/http/tests/worklet/chromium/import-on-detached-iframe.html
[modify] https://crrev.com/bc9dd77abc396e48a6de5b0b1ea9a34c6953cb5a/third_party/WebKit/LayoutTests/http/tests/worklet/chromium/worklet-should-report-context-destroyed.html
[modify] https://crrev.com/bc9dd77abc396e48a6de5b0b1ea9a34c6953cb5a/third_party/WebKit/LayoutTests/http/tests/worklet/paint-worklet-import.html
[modify] https://crrev.com/bc9dd77abc396e48a6de5b0b1ea9a34c6953cb5a/third_party/WebKit/LayoutTests/http/tests/worklet/webexposed/global-interface-listing-paint-worklet.html
[modify] https://crrev.com/bc9dd77abc396e48a6de5b0b1ea9a34c6953cb5a/third_party/WebKit/LayoutTests/webexposed/global-interface-listing-expected.txt
[modify] https://crrev.com/bc9dd77abc396e48a6de5b0b1ea9a34c6953cb5a/third_party/WebKit/Source/bindings/core/v8/V8BindingForCore.h
[modify] https://crrev.com/bc9dd77abc396e48a6de5b0b1ea9a34c6953cb5a/third_party/WebKit/Source/core/core_idl_files.gni
[modify] https://crrev.com/bc9dd77abc396e48a6de5b0b1ea9a34c6953cb5a/third_party/WebKit/Source/modules/csspaint/BUILD.gn
[modify] https://crrev.com/bc9dd77abc396e48a6de5b0b1ea9a34c6953cb5a/third_party/WebKit/Source/modules/csspaint/CSSPaintImageGeneratorImpl.cpp
[add] https://crrev.com/bc9dd77abc396e48a6de5b0b1ea9a34c6953cb5a/third_party/WebKit/Source/modules/csspaint/CSSPaintWorklet.cpp
[add] https://crrev.com/bc9dd77abc396e48a6de5b0b1ea9a34c6953cb5a/third_party/WebKit/Source/modules/csspaint/CSSPaintWorklet.h
[rename] https://crrev.com/bc9dd77abc396e48a6de5b0b1ea9a34c6953cb5a/third_party/WebKit/Source/modules/csspaint/CSSPaintWorklet.idl
[modify] https://crrev.com/bc9dd77abc396e48a6de5b0b1ea9a34c6953cb5a/third_party/WebKit/Source/modules/csspaint/PaintWorklet.cpp
[modify] https://crrev.com/bc9dd77abc396e48a6de5b0b1ea9a34c6953cb5a/third_party/WebKit/Source/modules/csspaint/PaintWorklet.h
[modify] https://crrev.com/bc9dd77abc396e48a6de5b0b1ea9a34c6953cb5a/third_party/WebKit/Source/modules/csspaint/PaintWorkletGlobalScope.cpp
[modify] https://crrev.com/bc9dd77abc396e48a6de5b0b1ea9a34c6953cb5a/third_party/WebKit/Source/modules/csspaint/PaintWorkletTest.cpp
[delete] https://crrev.com/1a5027db2e06101357abd3563bce7f8284e0932d/third_party/WebKit/Source/modules/csspaint/WindowPaintWorklet.cpp
[delete] https://crrev.com/1a5027db2e06101357abd3563bce7f8284e0932d/third_party/WebKit/Source/modules/csspaint/WindowPaintWorklet.h
[modify] https://crrev.com/bc9dd77abc396e48a6de5b0b1ea9a34c6953cb5a/third_party/WebKit/Source/modules/modules_idl_files.gni