tree a864bfaf00a8e44660dbcb10dfca4f1009a78a76
parent d6c156f2a063659b13b031e8888838b34bf0d4a6
author Xida Chen <xidachen@chromium.org> 1610118581 -0800
committer Blink WPT Bot <blink-w3c-test-autoroller@chromium.org> 1610119758 -0800

Keep offset for composite background color animation

At this moment, our implementation only keeps the first and the
last keyframes for composite background color animation. This is
wrong, for example, we can having multiple keyframes like:
0%: { background-color: red }
10%: { background-color: green}
100% { background-color: blue}

This CL fixes the issue. The idea is to keep the offset which
we stored in CompositorKeyframeValues. In the above case, the
offsets would be [0, 0.1, 1].

Once we have that, here is how we do interpolation. Say that
the current progress is 0.4, then we know that it falls in to
the range of [0.1, 1], which means we need to interpolate from
green to blue. We need to adjust the progress (0.4) based on the
offsets. Basically scale [0.1, 1] to [0, 1], then the adjusted
progress should be (0.4-0.1) / (1-0.1). Layout tests are added
to ensure correctness.

Bug: 1153671
Change-Id: I6dffc82b5821fdf418f2b94331f567a239079730
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2597844
Commit-Queue: Xida Chen <xidachen@chromium.org>
Reviewed-by: Kevin Ellis <kevers@chromium.org>
Cr-Commit-Position: refs/heads/master@{#841476}