Define WebScrollOffsetAnimationCurveImpl

Define WebScrollOffsetAnimationCurveImpl

This defines WebScrollOffsetAnimationCurveImpl, which wraps a
cc::ScrollOffsetAnimationCurve. This is needed for
implementing the CSSOM Smooth Scroll API.

BUG=243871
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=245645

[ajuma, 2014-01-14 17:54:05]

The Blink side of this change is part of http://crrev.com/134443003.

[Ian Vollick, 2014-01-17 13:53:44]

On 2014/01/14 17:54:05, ajuma wrote:
> The Blink side of this change is part of http://crrev.com/134443003.

cc/ lgtm and webkit/ lg2m.

[ajuma, 2014-01-17 14:04:16]

+jamesr for webkit/

[jamesr, 2014-01-17 20:42:24]

Why does a scroll offset animation need a new curve type?  Wouldn't it just be
one of the existing curve types targetting a different property?

[ajuma, 2014-01-17 20:53:30]

On 2014/01/17 20:42:24, jamesr wrote:
> Why does a scroll offset animation need a new curve type?  Wouldn't it just be
> one of the existing curve types targetting a different property?

The duration and initial value of a scroll offset animation, unlike other
animations we support, aren't provided ahead of time; instead, the initial value
is set at commit time to the current scroll offset. Then, the duration is
calculated based on the delta in both the x and y directions. This means that
simply using two float animation curves (one for each direction) for a scroll
animation would be awkward, since we don't really have two independent
animations.

[jamesr, 2014-01-17 21:02:02]

seems unfortunate that we can't build this out of existing primitives :(

lgtm

[commit-bot: I haz the power, 2014-01-17 21:05:42]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/ajuma@chromium.org/112933005/70001

[commit-bot: I haz the power, 2014-01-17 22:37:29]

Change committed as 245645