[SP] Don't invalidate the whole scrolled tree

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 e22534da688657165f6e1e08a74ed66aac68d8f3..b04e90d779ee783168fff559d18f391fcfe7aa77 100644
--- a/Source/core/paint/DeprecatedPaintLayerScrollableArea.cpp
+++ b/Source/core/paint/DeprecatedPaintLayerScrollableArea.cpp
@@ -424,13 +424,8 @@ void DeprecatedPaintLayerScrollableArea::setScrollOffset(const DoublePoint& newS
             requiresPaintInvalidation = true;
     }
 
-    // For slimming paint we need to fully invalidate during scrolling.
-    if (requiresPaintInvalidation && RuntimeEnabledFeatures::slimmingPaintEnabled()) {
-        DisablePaintInvalidationStateAsserts disabler;
-        box().invalidatePaintIncludingNonCompositingDescendants();
-    }
-
     // Just schedule a full paint invalidation of our object.
+    // FIXME: This invalidation will be unnecessary in slimming paint phase 2.
     if (requiresPaintInvalidation)
         box().setShouldDoFullPaintInvalidation();