Gecko has moved the functionality to a different mixin, so does still support it. https://developer.mozilla.org/en-US/docs/Web/API/ImageBitmapFactories

The question then is whether we should support the WindowOrWorkerGlobalScope mixin: https://developer.mozilla.org/en-US/docs/Web/API/WindowOrWorkerGlobalScope

The current HTML doesn't define ImageBitmapFactories on the WindowOrWorkerGlobalScope mixin:
https://html.spec.whatwg.org/multipage/webappapis.html#windoworworkerglobalscope-mixin

Was it deprecated in favor of createImageBitmap? Who knows the current status of the ImageBitmap spec?

The createImageBitmap methods were moved from the ImageBitmapFactories mix-in to the (newly formed) WindowOrWorkerGlobalScope mix-in by:

https://github.com/whatwg/html/commit/cdd48e1f570c817402bf62108847c4a9f4b00b1e

we're currently missing the latter ("newer") though. The situation should be similar for btoa/atob and other things that got relocated in the commit above.

Is the change in mix-in observable in JS?  AFAICT, either way createImageBitmap is a member of Window and of WorkerGlobalScope.

The current situation shouldn't be a problem I think. Not having WindowOrWorkerGlobalScope is probably more so (from a development PoV.)

Since https://codereview.chromium.org/2798433003/ links to this bug, I've treated it as the "add WindowOrWorkerGlobalScope mix-in" bug and blocked some other things on it.

Now we have core/frame/window_or_worker_global_scope.idl

I'd like to work on it.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/0b2bc0cdfb3a2736bbc573f15009d4ee4ab969cf

commit 0b2bc0cdfb3a2736bbc573f15009d4ee4ab969cf
Author: Amos Lim <eui-sang.lim@samsung.com>
Date: Thu Nov 29 08:11:08 2018

Merge ImageBitmapFactories into WindowOrWorkerGlobalScope mix-in

According to the spec, the createImageBitmap should be moved
to WindowOrWorkerGlobalScope mix-in.

They were moved from the ImageBitmapFactories mix-in
to the WindowOrWorkerGlobalScope mix-in[1].

[1]: https://github.com/whatwg/html/commit/cdd48e1f570c817402bf62108847c4a9f4b00b1e
[2]: https://html.spec.whatwg.org/multipage/webappapis.html#windoworworkerglobalscope-mixin

This CL has no behavior changes.

Bug:  701457 
Change-Id: Idbf0cf3e22019cc24384ab3c409e202343eb1d5a
Reviewed-on: https://chromium-review.googlesource.com/c/1349160
Commit-Queue: Amos Lim <eui-sang.lim@samsung.com>
Reviewed-by: Kent Tamura <tkent@chromium.org>
Reviewed-by: Yuki Shiino <yukishiino@chromium.org>
Reviewed-by: Fernando Serboncini <fserb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#612095}
[modify] https://crrev.com/0b2bc0cdfb3a2736bbc573f15009d4ee4ab969cf/third_party/blink/renderer/bindings/scripts/utilities.py
[modify] https://crrev.com/0b2bc0cdfb3a2736bbc573f15009d4ee4ab969cf/third_party/blink/renderer/core/core_idl_files.gni
[modify] https://crrev.com/0b2bc0cdfb3a2736bbc573f15009d4ee4ab969cf/third_party/blink/renderer/core/frame/window_or_worker_global_scope.cc
[modify] https://crrev.com/0b2bc0cdfb3a2736bbc573f15009d4ee4ab969cf/third_party/blink/renderer/core/frame/window_or_worker_global_scope.h
[modify] https://crrev.com/0b2bc0cdfb3a2736bbc573f15009d4ee4ab969cf/third_party/blink/renderer/core/frame/window_or_worker_global_scope.idl
[modify] https://crrev.com/0b2bc0cdfb3a2736bbc573f15009d4ee4ab969cf/third_party/blink/renderer/core/imagebitmap/image_bitmap_factories.cc
[modify] https://crrev.com/0b2bc0cdfb3a2736bbc573f15009d4ee4ab969cf/third_party/blink/renderer/core/imagebitmap/image_bitmap_factories.h
[delete] https://crrev.com/32be36c36cb3f33b01e4ad2a8d7f786b77ebcdba/third_party/blink/renderer/core/imagebitmap/image_bitmap_factories.idl
[modify] https://crrev.com/0b2bc0cdfb3a2736bbc573f15009d4ee4ab969cf/third_party/blink/renderer/modules/shapedetection/shape_detector.h