SP: Invalidate all non-compositing descendants in the slow scroll path.

Source/core/paint/DeprecatedPaintLayerScrollableArea.cpp

Index: Source/core/paint/DeprecatedPaintLayerScrollableArea.cpp
diff --git a/Source/core/paint/DeprecatedPaintLayerScrollableArea.cpp b/Source/core/paint/DeprecatedPaintLayerScrollableArea.cpp
index 6a672254dcdb0bcf693770515930213de0a8d0de..bb3d55ce33746ecf121ab814f27c981cc85ba63f 100644
--- a/Source/core/paint/DeprecatedPaintLayerScrollableArea.cpp
+++ b/Source/core/paint/DeprecatedPaintLayerScrollableArea.cpp
@@ -424,8 +424,12 @@ void DeprecatedPaintLayerScrollableArea::setScrollOffset(const DoublePoint& newS
 
     // Just schedule a full paint invalidation of our object.
     // FIXME: This invalidation will be unnecessary in slimming paint phase 2.
-    if (requiresPaintInvalidation)
-        box().setShouldDoFullPaintInvalidation();
+    if (requiresPaintInvalidation) {
+        if (RuntimeEnabledFeatures::slimmingPaintEnabled())
+            box().setShouldDoFullPaintInvalidationIncludingNonCompositingDescendants();
+        else
+            box().setShouldDoFullPaintInvalidation();
+    }
 
     // Schedule the scroll DOM event.
     if (box().node())