Correctly update scroll offset animations in response to scroll anchoring

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/line/InlineTextBox.h"
 #include "core/paint/PaintLayerScrollableArea.h"
@@ skipping 224 matching lines @@
         m_lastAdjustment = IntSize();
         m_lastAdjusted.clear();
         return;
     }
     adjust(adjustment);
 }
 
 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()) {
+
+    if (!animator)
         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();
-        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();
         m_lastAdjusted = m_current;
     }
     m_hasBounced = (m_lastAdjustment == -adjustment);
     m_lastAdjustment = adjustment;
 
     // Update UMA metric.
     DEFINE_STATIC_LOCAL(EnumerationHistogram, adjustedOffsetHistogram,
@@ skipping 24 matching lines @@
 
 void ScrollAnchor::notifyRemoved(LayoutObject* layoutObject)
 {
     if (m_current.m_anchorObject == layoutObject)
         m_current.clear();
     if (m_lastAdjusted.m_anchorObject == layoutObject)
         m_lastAdjusted.clear();
 }
 
 } // namespace blink