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, 14 insertions, 5 deletions

diff --git a/third_party/WebKit/Source/platform/scroll/ScrollAnimator.h b/third_party/WebKit/Source/platform/scroll/ScrollAnimator.h
index 01746e68..5d8f20a 100644
--- a/third_party/WebKit/Source/platform/scroll/ScrollAnimator.h
+++ b/third_party/WebKit/Source/platform/scroll/ScrollAnimator.h
@@ -34,11 +34,14 @@
 #include "platform/Timer.h"
 #include "platform/geometry/FloatPoint.h"
 #include "platform/scroll/ScrollAnimatorBase.h"
+#include "public/platform/WebCompositorAnimationDelegate.h"
+#include "public/platform/WebCompositorAnimationPlayerClient.h"
 #include "public/platform/WebScrollOffsetAnimationCurve.h"
 
 namespace blink {
 
 class ScrollAnimatorTest;
+class WebCompositorAnimationTimeline;
 
 class PLATFORM_EXPORT ScrollAnimator final : public ScrollAnimatorBase {
 public:
@@ -50,20 +53,26 @@ public:
     ScrollResultOneDimensional userScroll(ScrollbarOrientation, ScrollGranularity, float step, float delta) override;
     void scrollToOffsetWithoutAnimation(const FloatPoint&) override;
 
-    void cancelAnimations() override;
-    void serviceScrollAnimations() override;
-    bool hasRunningAnimation() const override;
+    // ScrollAnimatorCompositorCoordinator implementation.
+    void tickAnimation(double monotonicTime) override;
+    void cancelAnimation() override;
+    void resetAnimationState() override;
+    void updateCompositorAnimations() override;
+    void notifyCompositorAnimationFinished(int groupId) override;
+    void layerForCompositedScrollingDidChange(WebCompositorAnimationTimeline*) override;
 
     DECLARE_VIRTUAL_TRACE();
 
 protected:
-    void animationTimerFired();
-
     OwnPtr<WebScrollOffsetAnimationCurve> m_animationCurve;
+    double m_lastTickTime;
     double m_startTime;
     WTF::TimeFunction m_timeFunction;
+
 private:
     FloatPoint desiredTargetPosition() const;
+
+    FloatPoint m_targetOffset;
 };
 
 } // namespace blink