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

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

Index: third_party/WebKit/Source/core/frame/FrameView.cpp
diff --git a/third_party/WebKit/Source/core/frame/FrameView.cpp b/third_party/WebKit/Source/core/frame/FrameView.cpp
index c2bc13f9d104dfbd0107264d59ce9fdebe2ac1a5..e634f3d220955d8950297580c2e3f33d1ff669a4 100644
--- a/third_party/WebKit/Source/core/frame/FrameView.cpp
+++ b/third_party/WebKit/Source/core/frame/FrameView.cpp
@@ -1410,10 +1410,8 @@ bool FrameView::invalidateViewportConstrainedObjects()
         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"),
@@ -1422,7 +1420,10 @@ bool FrameView::invalidateViewportConstrainedObjects()
             "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;
 }