Invalidate fixed-pos elements & descendants on scroll w/filters that change pixels.

third_party/WebKit/Source/core/frame/FrameView.cpp

 /*
  * Copyright (C) 1998, 1999 Torben Weis <weis@kde.org>
  *                     1999 Lars Knoll <knoll@kde.org>
  *                     1999 Antti Koivisto <koivisto@kde.org>
  *                     2000 Dirk Mueller <mueller@kde.org>
  * Copyright (C) 2004, 2005, 2006, 2007, 2008 Apple Inc. All rights reserved.
  *           (C) 2006 Graham Dennis (graham.dennis@gmail.com)
  *           (C) 2006 Alexey Proskuryakov (ap@nypop.com)
  * Copyright (C) 2009 Google Inc. All rights reserved.
  *
@@ skipping 1379 matching lines @@
         ASSERT(layoutItem.style()->hasViewportConstrainedPosition());
         ASSERT(layoutItem.hasLayer());
         PaintLayer* layer = LayoutBoxModel(layoutItem).layer();
 
         if (layer->isPaintInvalidationContainer())
             continue;
 
         if (layer->subtreeIsInvisible())
             continue;
 
-        // If the fixed layer has a blur/drop-shadow filter applied on at least one of its parents, we cannot
-        // scroll using the fast path, otherwise the outsets of the filter will be moved around the page.
-        if (layer->hasAncestorWithFilterThatMovesPixels())
-            return false;
+        // invalidate even if there is an ancestor with a filter that moves pixels.
+        layoutItem.setShouldDoFullPaintInvalidationIncludingNonCompositingDescendants();
 
         TRACE_EVENT_INSTANT1(
             TRACE_DISABLED_BY_DEFAULT("devtools.timeline.invalidationTracking"),
             "ScrollInvalidationTracking",
             TRACE_EVENT_SCOPE_THREAD,
             "data",
             InspectorScrollInvalidationTrackingEvent::data(*layoutObject));
 
-        layoutItem.setShouldDoFullPaintInvalidationIncludingNonCompositingDescendants();
+        // If the fixed layer has a blur/drop-shadow filter applied on at least one of its parents, we cannot
+        // scroll using the fast path, otherwise the outsets of the filter will be moved around the page.
+        if (layer->hasAncestorWithFilterThatMovesPixels())
+            return false;
     }
     return true;
 }
 
 bool FrameView::scrollContentsFastPath(const IntSize& scrollDelta)
 {
     if (!contentsInCompositedLayer())
         return false;
 
     invalidateBackgroundAttachmentFixedObjects();
@@ skipping 2698 matching lines @@
     return m_subtreeThrottled || (m_hiddenForThrottling && m_crossOriginForThrottling);
 }
 
 LayoutBox& FrameView::boxForScrollControlPaintInvalidation() const
 {
     ASSERT(layoutView());
     return *layoutView();
 }
 
 } // namespace blink