Hi. Spec editor there. The fact that you can both have `auto` compute to itself as a keyword and still have it animate is an interesting possibility that I had not considered.

I've opened https://github.com/w3c/csswg-drafts/issues/781 to discuss with the CSS Working Group.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/3ddca0e44883c2ae38bcc45b48853d0db31e9691

commit 3ddca0e44883c2ae38bcc45b48853d0db31e9691
Author: rego <rego@igalia.com>
Date: Thu Dec 22 10:42:12 2016

[css-ui] Make caret-color animatable

This patch makes caret-color an animatable property.
The only special part is becuase "auto", the initial value of
this property, is not interpolable, so we need to do some changes in
CSSAnimatableValueFactory::create() and ColorPropertyFunctions.
Also this patch modifies StyleAutoColor, so toStyleColor()
can only be called for non "auto" colors.

Adds 2 new tests (caret-color-composition.html and
caret-color-interpolation.html) to verify that
the interpolation works as expected.
Also the animations tests (caret-color-018.html and
caret-color-020.html) from the W3C suite are passing now.
Marks caret-color-021.html as failing because of the TODOs
on the patch (see  http://crbug.com/676295 ).

BUG= 669490 
TEST=animations/composition/caret-color-composition.html
TEST=animations/interpolation/caret-color-interpolation.html
TEST=imported/csswg-test/css-ui-3/caret-color-018.html
TEST=imported/csswg-test/css-ui-3/caret-color-019.html
TEST=imported/csswg-test/css-ui-3/caret-color-020.html

Review-Url: https://codereview.chromium.org/2537373005
Cr-Commit-Position: refs/heads/master@{#440377}

[modify] https://crrev.com/3ddca0e44883c2ae38bcc45b48853d0db31e9691/third_party/WebKit/LayoutTests/TestExpectations
[add] https://crrev.com/3ddca0e44883c2ae38bcc45b48853d0db31e9691/third_party/WebKit/LayoutTests/animations/composition/caret-color-composition.html
[add] https://crrev.com/3ddca0e44883c2ae38bcc45b48853d0db31e9691/third_party/WebKit/LayoutTests/animations/interpolation/caret-color-interpolation.html
[add] https://crrev.com/3ddca0e44883c2ae38bcc45b48853d0db31e9691/third_party/WebKit/LayoutTests/imported/csswg-test/css-ui-3/caret-color-021.html
[modify] https://crrev.com/3ddca0e44883c2ae38bcc45b48853d0db31e9691/third_party/WebKit/Source/core/animation/CSSColorInterpolationType.cpp
[modify] https://crrev.com/3ddca0e44883c2ae38bcc45b48853d0db31e9691/third_party/WebKit/Source/core/animation/CSSInterpolationTypesMap.cpp
[modify] https://crrev.com/3ddca0e44883c2ae38bcc45b48853d0db31e9691/third_party/WebKit/Source/core/animation/ColorPropertyFunctions.cpp
[modify] https://crrev.com/3ddca0e44883c2ae38bcc45b48853d0db31e9691/third_party/WebKit/Source/core/animation/ColorPropertyFunctions.h
[modify] https://crrev.com/3ddca0e44883c2ae38bcc45b48853d0db31e9691/third_party/WebKit/Source/core/animation/css/CSSAnimatableValueFactory.cpp
[modify] https://crrev.com/3ddca0e44883c2ae38bcc45b48853d0db31e9691/third_party/WebKit/Source/core/css/CSSProperties.in
[modify] https://crrev.com/3ddca0e44883c2ae38bcc45b48853d0db31e9691/third_party/WebKit/Source/core/css/StyleAutoColor.h
[modify] https://crrev.com/3ddca0e44883c2ae38bcc45b48853d0db31e9691/third_party/WebKit/Source/core/css/resolver/AnimatedStyleBuilder.cpp
[modify] https://crrev.com/3ddca0e44883c2ae38bcc45b48853d0db31e9691/third_party/WebKit/Source/core/style/ComputedStyle.cpp

 Bug #676295  has been fixed so now this is done.