RenderLayerScrollableArea::updateScrollCornerStyle shouldn't do work if we're using overlay scrollb…

Source/core/rendering/RenderLayerScrollableArea.cpp

 /*
  * Copyright (C) 2006, 2007, 2008, 2009, 2010, 2011, 2012 Apple Inc. All rights reserved.
  *
  * Portions are Copyright (C) 1998 Netscape Communications Corporation.
  *
  * Other contributors:
  *   Robert O'Callahan <roc+@cs.cmu.edu>
  *   David Baron <dbaron@fas.harvard.edu>
  *   Christian Biesinger <cbiesinger@web.de>
  *   Randall Jesup <rjesup@wgate.com>
@@ skipping 583 matching lines @@
     // overflow:auto may need to lay out again if scrollbars got added/removed.
     bool autoHorizontalScrollBarChanged = m_box->hasAutoHorizontalScrollbar() && (hasHorizontalScrollbar() != hasHorizontalOverflow);
     bool autoVerticalScrollBarChanged = m_box->hasAutoVerticalScrollbar() && (hasVerticalScrollbar() != hasVerticalOverflow);
 
     if (autoHorizontalScrollBarChanged || autoVerticalScrollBarChanged) {
         if (m_box->hasAutoHorizontalScrollbar())
             setHasHorizontalScrollbar(hasHorizontalOverflow);
         if (m_box->hasAutoVerticalScrollbar())
             setHasVerticalScrollbar(hasVerticalOverflow);
 
+        if (hasVerticalOverflow || hasHorizontalOverflow)
+            updateScrollCornerStyle();
+
         layer()->updateSelfPaintingLayer();
 
         // Force an update since we know the scrollbars have changed things.
         if (m_box->document().hasAnnotatedRegions())
             m_box->document().setAnnotatedRegionsDirty(true);
 
         if (!RuntimeEnabledFeatures::repaintAfterLayoutEnabled())
             m_box->repaint();
 
         if (m_box->style()->overflowX() == OAUTO || m_box->style()->overflowY() == OAUTO) {
@@ skipping 337 matching lines @@
 bool RenderLayerScrollableArea::scrollsOverflow() const
 {
     if (FrameView* frameView = m_box->view()->frameView())
         return frameView->containsScrollableArea(this);
 
     return false;
 }
 
 void RenderLayerScrollableArea::updateScrollCornerStyle()
 {
+    if (!m_scrollCorner && !hasScrollbar())
+        return;
+    if (!m_scrollCorner && hasOverlayScrollbars())
+        return;
+
     RenderObject* actualRenderer = rendererForScrollbar(m_box);
     RefPtr<RenderStyle> corner = m_box->hasOverflowClip() ? actualRenderer->getUncachedPseudoStyle(PseudoStyleRequest(SCROLLBAR_CORNER), actualRenderer->style()) : PassRefPtr<RenderStyle>(nullptr);
     if (corner) {
         if (!m_scrollCorner) {
             m_scrollCorner = RenderScrollbarPart::createAnonymous(&m_box->document());
             m_scrollCorner->setParent(m_box);
         }
         m_scrollCorner->setStyle(corner.release());
     } else if (m_scrollCorner) {
         m_scrollCorner->destroy();
@@ skipping 552 matching lines @@
 void RenderLayerScrollableArea::setForceNeedsCompositedScrolling(ForceNeedsCompositedScrollingMode mode)
 {
     if (m_forceNeedsCompositedScrolling == mode)
         return;
 
     m_forceNeedsCompositedScrolling = mode;
     layer()->didUpdateNeedsCompositedScrolling();
 }
 
 } // Namespace WebCore