Don't use pairwise keyframe interpolation at fractions 0 and 1.

Don't use pairwise keyframe interpolation at fractions 0 and 1.

This change modifies InvalidatableStyleInterpolations to treat fractions
0 and 1 as non-pairwise. At these fractions only the respective start or
end keyframe will be used to produce an InterpolationValue.

This change prevents us from using features from both keyframes when
only one should apply at these fractions.

Example:
element.animate([{
  backgroundImage: 'url(a), url(b)',
}, {
  backgroundImage: 'url(c)',
}, {
  duration: 1000,
  fill: 'forwards',
});
This animation should fill forwards as 'url(c)' and not 'url(c), url(c)'.

BUG=442163
Committed: https://crrev.com/70ab39994327394f7df9ae8d5aab8db76a114ea3
Cr-Commit-Position: refs/heads/master@{#353939}

[alancutter (OOO until 2018), 2015-10-02 03:44:43]

alancutter@chromium.org changed reviewers:
+ dstockwell@chromium.org

[dstockwell, 2015-10-02 03:55:58]

lgtm

https://codereview.chromium.org/1379263002/diff/1/third_party/WebKit/Source/c...
File third_party/WebKit/Source/core/animation/InvalidatableStyleInterpolation.h
(right):

https://codereview.chromium.org/1379263002/diff/1/third_party/WebKit/Source/c...
third_party/WebKit/Source/core/animation/InvalidatableStyleInterpolation.h:45: ,
m_isCachePending(true)
Perhaps invert this, m_isCached?

[alancutter (OOO until 2018), 2015-10-08 05:18:49]

https://codereview.chromium.org/1379263002/diff/1/third_party/WebKit/Source/c...
File third_party/WebKit/Source/core/animation/InvalidatableStyleInterpolation.h
(right):

https://codereview.chromium.org/1379263002/diff/1/third_party/WebKit/Source/c...
third_party/WebKit/Source/core/animation/InvalidatableStyleInterpolation.h:45: ,
m_isCachePending(true)
On 2015/10/02 at 03:55:58, dstockwell wrote:
> Perhaps invert this, m_isCached?

Done.

[alancutter (OOO until 2018), 2015-10-14 00:04:43]

The CQ bit was checked by alancutter@chromium.org

[alancutter (OOO until 2018), 2015-10-14 00:04:44]

The patchset sent to the CQ was uploaded after l-g-t-m from
dstockwell@chromium.org
Link to the patchset: https://codereview.chromium.org/1379263002/#ps40001
(title: "Rebase")

[commit-bot: I haz the power, 2015-10-14 00:06:37]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1379263002/40001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1379263002/40001

[commit-bot: I haz the power, 2015-10-14 02:13:41]

Committed patchset #3 (id:40001)

[commit-bot: I haz the power, 2015-10-14 02:14:30]

Patchset 3 (id:??) landed as
https://crrev.com/70ab39994327394f7df9ae8d5aab8db76a114ea3
Cr-Commit-Position: refs/heads/master@{#353939}