Return reference from styleEngine() accessor.

Source/core/frame/FrameView.cpp

 /*
  * Copyright (C) 1998, 1999 Torben Weis <weis@kde.org>
  *                     1999 Lars Knoll <knoll@kde.org>
  *                     1999 Antti Koivisto <koivisto@kde.org>
  *                     2000 Dirk Mueller <mueller@kde.org>
  * Copyright (C) 2004, 2005, 2006, 2007, 2008 Apple Inc. All rights reserved.
  *           (C) 2006 Graham Dennis (graham.dennis@gmail.com)
  *           (C) 2006 Alexey Proskuryakov (ap@nypop.com)
  * Copyright (C) 2009 Google Inc. All rights reserved.
  *
@@ skipping 319 matching lines @@
     }
     if (didStyleChange) {
         updateScrollbarGeometry();
         updateScrollCorner();
         positionScrollbarLayers();
     }
 }
 
 void FrameView::invalidateAllCustomScrollbarsOnActiveChanged()
 {
-    bool usesWindowInactiveSelector = m_frame->document()->styleEngine()->usesWindowInactiveSelector();
+    bool usesWindowInactiveSelector = m_frame->document()->styleEngine().usesWindowInactiveSelector();
 
     const ChildrenWidgetSet* viewChildren = children();
     for (const RefPtrWillBeMember<Widget>& child : *viewChildren) {
         Widget* widget = child.get();
         if (widget->isFrameView())
             toFrameView(widget)->invalidateAllCustomScrollbarsOnActiveChanged();
         else if (usesWindowInactiveSelector && widget->isScrollbar() && toScrollbar(widget)->isCustomScrollbar())
             toScrollbar(widget)->styleChanged();
     }
     if (usesWindowInactiveSelector)
@@ skipping 3748 matching lines @@
 {
     Settings* settings = frame().settings();
     if (!settings || !settings->rootLayerScrolls())
         return this;
 
     LayoutView* layoutView = this->layoutView();
     return layoutView ? layoutView->scrollableArea() : nullptr;
 }
 
 } // namespace blink