The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/fdda0c9d6a6853789e9558364e8045acbaa260dc

commit fdda0c9d6a6853789e9558364e8045acbaa260dc
Author: Darren Shen <shend@chromium.org>
Date: Thu Feb 22 03:20:14 2018

[css-typed-om] Allow CSSVariableReferenceValue.fallback to be nullable.

Spec change:
https://github.com/w3c/css-houdini-drafts/commit/c9d9c29889fed7a65c1bf029b65320d3f43b1baa

Bug:  814487 
Change-Id: Idb15d8edc4dc7aba4cf40ac13b69ea13ef7d8f60
Reviewed-on: https://chromium-review.googlesource.com/930102
Commit-Queue: Darren Shen <shend@chromium.org>
Reviewed-by: nainar <nainar@chromium.org>
Cr-Commit-Position: refs/heads/master@{#538328}
[modify] https://crrev.com/fdda0c9d6a6853789e9558364e8045acbaa260dc/third_party/WebKit/LayoutTests/external/wpt/css/css-typed-om/stylevalue-subclasses/cssVariableReferenceValue.html
[modify] https://crrev.com/fdda0c9d6a6853789e9558364e8045acbaa260dc/third_party/WebKit/LayoutTests/external/wpt/interfaces/css-typed-om.idl
[modify] https://crrev.com/fdda0c9d6a6853789e9558364e8045acbaa260dc/third_party/WebKit/Source/core/css/cssom/CSSVariableReferenceValue.idl

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/d0479df6e33782088e8568d3e020d6a6155269ce

commit d0479df6e33782088e8568d3e020d6a6155269ce
Author: Darren Shen <shend@chromium.org>
Date: Thu Feb 22 23:56:12 2018

[css-typed-om] Give default value for CSSVariableReferenceValue.fallback

The spec gave a default value for CSSVariableReferenceValue.fallback:
https://github.com/w3c/css-houdini-drafts/commit/372f85caa48a713f8c683d34a59dc3ceb0839d79

No observable changes to behaviour.

Bug:  814487 
Change-Id: Id33f16167c8b8d9eac3fb70ce7e817de659c7465
Reviewed-on: https://chromium-review.googlesource.com/932921
Reviewed-by: nainar <nainar@chromium.org>
Commit-Queue: Darren Shen <shend@chromium.org>
Cr-Commit-Position: refs/heads/master@{#538623}
[modify] https://crrev.com/d0479df6e33782088e8568d3e020d6a6155269ce/third_party/WebKit/LayoutTests/external/wpt/interfaces/css-typed-om.idl
[modify] https://crrev.com/d0479df6e33782088e8568d3e020d6a6155269ce/third_party/WebKit/Source/core/css/cssom/CSSVariableReferenceValue.idl