Reland of un smooth scroll animations on the compositor when possible (patchset #1 id:1 of https://codereview.chromium.org/1548883002/ )

Reason for revert:
The revert did not help, the tests

virtual/threaded/fast/scroll-behavior/overflow-scroll-root-frame-animates.html
virtual/threaded/fast/scroll-behavior/overflow-scroll-animates.html

are now slower and hitting test timeout limits.

Original issue's description:
> Revert of Run smooth scroll animations on the compositor when possible (patchset #4 id:60001 of https://codereview.chromium.org/1534813004/ )
>
> Reason for revert:
> Appears to have made Linux debug builds fail the following tests:
>
> virtual/threaded/fast/scroll-behavior/overflow-scroll-root-frame-animates.html
> virtual/threaded/fast/scroll-behavior/overflow-scroll-animates.html
>
> https://build.chromium.org/p/chromium.webkit/builders/WebKit%20Linux%20%28dbg%29/builds/5360
>
> Reverting to green the Blink tree.
>
> Original issue's description:
> > Run smooth scroll animations on the compositor when possible
> >
> > This CL implements "immediate retargeting" shown in the following diagram:
> > https://docs.google.com/drawings/d/1z76m-GMDgLI-clkfroLJ-5yhsHkmriZr_swP0kn5iw4
> >
> > This CL does the following
> > - Add a new state to ScrollAnimatorCompositorCoordinator to update the target
> > offset on the compositor
> > - Use the ScrollAnimatorCompositorCoordinator to schedule anim
> > - Add plumbing from the animators to the animation controller to abort
> > animations
> >
> > Sample test pages:
> > yashmalik.com/nested_scroll_mousewheel_listener.html
> > yashmalik.com/nested_scroll_mousewheel_listener_15ms_janky.html (tight loop in RAF)
> >
> > BUG=552556
> > CQ_INCLUDE_TRYBOTS=tryserver.blink:linux_blink_rel
> >
> > Committed: https://crrev.com/5534a2b2972534b523014c803e1e0e0541855cc7
> > Cr-Commit-Position: refs/heads/master@{#366685}
>
> TBR=skobes@chromium.org,ajuma@chromium.org,vollick@chromium.org,rbyers@chromium.org,ymalik@chromium.org
> NOPRESUBMIT=true
> NOTREECHECKS=true
> NOTRY=true
> BUG=552556
>
> Committed: https://crrev.com/51059d9d038aa255afdddfcbd3d418eb42b718ff
> Cr-Commit-Position: refs/heads/master@{#366733}

TBR=skobes@chromium.org,ajuma@chromium.org,vollick@chromium.org,rbyers@chromium.org,ymalik@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=552556

Review URL: https://codereview.chromium.org/1543043004

Cr-Commit-Position: refs/heads/master@{#366739}

1 files changed, 7 insertions, 0 deletions

diff --git a/third_party/WebKit/Source/platform/scroll/ProgrammaticScrollAnimator.cpp b/third_party/WebKit/Source/platform/scroll/ProgrammaticScrollAnimator.cpp
index 6910c4f..3e29f04 100644
--- a/third_party/WebKit/Source/platform/scroll/ProgrammaticScrollAnimator.cpp
+++ b/third_party/WebKit/Source/platform/scroll/ProgrammaticScrollAnimator.cpp
@@ -64,6 +64,12 @@ void ProgrammaticScrollAnimator::animateToOffset(FloatPoint offset)
     m_runState = RunState::WaitingToSendToCompositor;
 }
 
+void ProgrammaticScrollAnimator::cancelAnimation()
+{
+    ASSERT(m_runState != RunState::RunningOnCompositorButNeedsUpdate);
+    ScrollAnimatorCompositorCoordinator::cancelAnimation();
+}
+
 void ProgrammaticScrollAnimator::tickAnimation(double monotonicTime)
 {
     if (m_runState != RunState::RunningOnMainThread)
@@ -154,6 +160,7 @@ void ProgrammaticScrollAnimator::layerForCompositedScrollingDidChange(WebComposi
 
 void ProgrammaticScrollAnimator::notifyCompositorAnimationFinished(int groupId)
 {
+    ASSERT(m_runState != RunState::RunningOnCompositorButNeedsUpdate);
     ScrollAnimatorCompositorCoordinator::compositorAnimationFinished(groupId);
 }