Correctly update scroll offset animations in response to scroll anchoring

third_party/WebKit/Source/core/layout/ScrollAnchor.cpp

Index: third_party/WebKit/Source/core/layout/ScrollAnchor.cpp
diff --git a/third_party/WebKit/Source/core/layout/ScrollAnchor.cpp b/third_party/WebKit/Source/core/layout/ScrollAnchor.cpp
index 63b69a4cdaa949962a24bf21fab031e9f84fe681..060b08f9e9a2005a1bb42baeede4184a7312f47a 100644
--- a/third_party/WebKit/Source/core/layout/ScrollAnchor.cpp
+++ b/third_party/WebKit/Source/core/layout/ScrollAnchor.cpp
@@ -243,20 +243,11 @@ void ScrollAnchor::adjust(IntSize adjustment)
 {
     DoublePoint desiredPos = m_scroller->scrollPositionDouble() + adjustment;
     ScrollAnimatorBase* animator = m_scroller->existingScrollAnimator();

[skobes, 2016/05/27 17:58:30]

Could these five lines be reduced to

  m_scroller->scrollAnimator().adjustScrollPosition(adjustment,
AnchoringScroll);

? I can't think of a good reason to avoid creating the scroll animator here, and
ScrollAnimator can simply call setScrollPosition if there is no animation.

[ymalik, 2016/05/27 20:03:11]

Done.

-    if (!animator || !animator->hasRunningAnimation()) {
-        m_scroller->setScrollPosition(desiredPos, AnchoringScroll);
-        animator->adjustImplOnlyScrollOffsetAnimation(FloatSize(adjustment));
-    } else {
-        // If in the middle of a scroll animation, stop the animation, make
-        // the adjustment, and continue the animation on the pending delta.
-        // TODO(skobes): This is not quite right, we are starting a new curve without
-        // saving our progress on the existing curve.
-        FloatSize pendingDelta = animator->desiredTargetPosition() -
-            FloatPoint(m_scroller->scrollPositionDouble());
-        animator->cancelAnimation();
+
+    if (!animator)
         m_scroller->setScrollPosition(desiredPos, AnchoringScroll);
-        animator->userScroll(ScrollByPixel, pendingDelta);
-    }
+    else
+        animator->adjustAnimationAndSetScrollPosition(adjustment, AnchoringScroll);
 
     if (m_current && m_lastAdjusted.m_anchorObject != m_current.m_anchorObject) {
         m_lastAdjusted.clear();