Communicate MT changes to impl-only scroll offset animations

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

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "core/layout/ScrollAnchor.h"
 
 #include "core/frame/FrameView.h"
 #include "core/frame/UseCounter.h"
 #include "core/layout/LayoutView.h"
 #include "core/layout/line/InlineTextBox.h"
@@ skipping 188 matching lines @@
     // should scroll by 1px instead of 0.2px.) This is true regardless of whether
     // the ScrollableArea actually uses fractional scroll positions.
     IntSize adjustment =
         roundedIntSize(computeRelativeOffset(m_anchorObject, m_scroller, m_corner)) -
         roundedIntSize(m_savedRelativeOffset);
     if (!adjustment.isZero()) {
         DoublePoint desiredPos = m_scroller->scrollPositionDouble() + adjustment;
         ScrollAnimatorBase* animator = m_scroller->existingScrollAnimator();
         if (!animator || !animator->hasRunningAnimation()) {
             m_scroller->setScrollPosition(desiredPos, AnchoringScroll);
+            animator->updateImplOnlyScrollOffsetAnimation(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.
             FloatSize pendingDelta = animator->desiredTargetPosition() - FloatPoint(m_scroller->scrollPositionDouble());
             animator->cancelAnimation();
             m_scroller->setScrollPosition(desiredPos, AnchoringScroll);
             animator->userScroll(ScrollByPixel, pendingDelta);
         }
         // Update UMA metric.
         DEFINE_STATIC_LOCAL(EnumerationHistogram, adjustedOffsetHistogram,
             ("Layout.ScrollAnchor.AdjustedScrollOffset", 2));
         adjustedOffsetHistogram.count(1);
         UseCounter::count(scrollerLayoutBox(m_scroller)->document(), UseCounter::ScrollAnchored);
     }
 }
 
 void ScrollAnchor::clear()
 {
     LayoutObject* anchorObject = m_anchorObject;
     m_anchorObject = nullptr;
 
     if (anchorObject)
         anchorObject->maybeClearIsScrollAnchorObject();
 }
 
 } // namespace blink