Fix behaviour of shadow interpolation with mismatched list lengths

Fix behaviour of shadow interpolation with mismatched list lengths

For shadow properties like box-shadow and text-shadow we were
incorrectly interpolating shadow lists with mismatched lengths.

The old behaviour would repeat each list to the lowest common multiple,
the correct behaviour is to pad the shorted list with "zero" shadows.

Spec: https://www.w3.org/TR/css3-transitions/#animatable-types

This change adds the "padding" behaviour to list interpolation and
composition and updates our shadow animation test cases to match
spec behaviour.

BUG=713674
Review-Url: https://codereview.chromium.org/2844213002
Cr-Commit-Position: refs/heads/master@{#470205}
(cherry picked from commit 4aaaf95a33ef49f61476ca1f3699700fa7ea3fe8)

Review-Url: https://codereview.chromium.org/2876723002 .
Cr-Commit-Position: refs/branch-heads/3071@{#506}
Cr-Branched-From: a106f0abbf69dad349d4aaf4bcc4f5d376dd2377-refs/heads/master@{#464641}
Committed: https://chromium.googlesource.com/chromium/src/+/ff1b1926fea47a35bfc0c9729a020ec20c8fa5f6

[alancutter (OOO until 2018), 2017-05-11 01:49:36]

Description was changed from

==========
Fix behaviour of shadow interpolation with mismatched list lengths

For shadow properties like box-shadow and text-shadow we were
incorrectly interpolating shadow lists with mismatched lengths.

The old behaviour would repeat each list to the lowest common multiple,
the correct behaviour is to pad the shorted list with "zero" shadows.

Spec: https://www.w3.org/TR/css3-transitions/#animatable-types

This change adds the "padding" behaviour to list interpolation and
composition and updates our shadow animation test cases to match
spec behaviour.

BUG=713674

Review-Url: https://codereview.chromium.org/2844213002
Cr-Commit-Position: refs/heads/master@{#470205}
(cherry picked from commit 4aaaf95a33ef49f61476ca1f3699700fa7ea3fe8)
==========

to

==========
Fix behaviour of shadow interpolation with mismatched list lengths

For shadow properties like box-shadow and text-shadow we were
incorrectly interpolating shadow lists with mismatched lengths.

The old behaviour would repeat each list to the lowest common multiple,
the correct behaviour is to pad the shorted list with "zero" shadows.

Spec: https://www.w3.org/TR/css3-transitions/#animatable-types

This change adds the "padding" behaviour to list interpolation and
composition and updates our shadow animation test cases to match
spec behaviour.

BUG=713674

Review-Url: https://codereview.chromium.org/2844213002
Cr-Commit-Position: refs/heads/master@{#470205}
(cherry picked from commit 4aaaf95a33ef49f61476ca1f3699700fa7ea3fe8)

Review-Url: https://codereview.chromium.org/2876723002 .
Cr-Commit-Position: refs/branch-heads/3071@{#506}
Cr-Branched-From:
a106f0abbf69dad349d4aaf4bcc4f5d376dd2377-refs/heads/master@{#464641}
Committed:
https://chromium.googlesource.com/chromium/src/+/ff1b1926fea47a35bfc0c9729a02...
==========

[alancutter (OOO until 2018), 2017-05-11 01:49:38]

Committed patchset #1 (id:1) manually as
ff1b1926fea47a35bfc0c9729a020ec20c8fa5f6.