CL:4497757 made the initial value of animation-duration auto,
but unfortunately reporting this auto value through getComputedStyle
broke existing web content (Issue 1452130).

Hence, hence the CSSWG opted to define a resolved value for
animation-duration, which converts auto to 0s unless we have some
non-default value for animation-timeline. This CL implements that
change.

This CL also contains a second change: reset-only sub-properties
of the 'animation' shorthand are now correctly set to their
initial value, or not some repeated amount of their initial value.
This change was necessary to prevent e.g. "animation: a1, a2"
from expanding to "animation-timeline: auto, auto", which would
disable the auto-to-0s conversion behavior.

Finally, note that the computedStyleMap (Typed OM) does not return
resolved values, but computed values. Hence it must not be affected
by the auto-to-0s conversion. To ensure this, an "override"
was added for kAnimationDuration in ComputedStyleUtils::
ComputedPropertyValue.

Bug: 1452130
Change-Id: I021ac68b61b83cd96962c56dab24043a19e99c5f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4607459


Commit-Queue: Anders Hartvoll Ruud <andruud@chromium.org>
Reviewed-by: Rune Lillesveen <futhark@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1157426}