[SP] Always paint whole non-custom scrollbars

Source/core/paint/ScrollableAreaPainter.cpp

 // Copyright 2014 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 "config.h"
 #include "core/paint/ScrollableAreaPainter.h"
 
 #include "core/layout/LayoutView.h"
 #include "core/page/Page.h"
 #include "core/paint/DeprecatedPaintLayer.h"
@@ skipping 150 matching lines @@
         return true;
 
     return false;
 }
 
 
 void ScrollableAreaPainter::paintScrollCorner(GraphicsContext* context, const IntPoint& paintOffset, const IntRect& damageRect)
 {
     IntRect absRect = m_scrollableArea.scrollCornerRect();
     absRect.moveBy(paintOffset);
-    if (!absRect.intersects(damageRect))
-        return;
 
     if (m_scrollableArea.scrollCorner()) {
+        if (!absRect.intersects(damageRect))
+            return;
         ScrollbarPainter::paintIntoRect(m_scrollableArea.scrollCorner(), context, paintOffset, LayoutRect(absRect));
         return;
     }
 
+    if (!RuntimeEnabledFeatures::slimmingPaintEnabled() && !absRect.intersects(damageRect))
+        return;
+
+    // We don't want to paint white if we have overlay scrollbars, since we need
+    // to see what is behind it.
+    if (m_scrollableArea.hasOverlayScrollbars())
+        return;
+
     DrawingRecorder recorder(*context, m_scrollableArea.box(), DisplayItem::ScrollbarCorner, absRect);
     if (recorder.canUseCachedDrawing())
         return;
 
-    // We don't want to paint white if we have overlay scrollbars, since we need
-    // to see what is behind it.
-    if (!m_scrollableArea.hasOverlayScrollbars())
-        context->fillRect(absRect, Color::white);
+    context->fillRect(absRect, Color::white);
 }
 
 } // namespace blink