Move the Widget hierarchy to the Oilpan heap.

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 340 matching lines @@
     }
 
     if (scrollOffset() == toIntSize(newScrollOffset))
         return;
 
     m_scrollOffset = toIntSize(newScrollOffset);
 
     LocalFrame* frame = box().frame();
     ASSERT(frame);
 
-    RefPtr<FrameView> frameView = box().frameView();
+    RefPtrWillBeRawPtr<FrameView> frameView = box().frameView();
 
     TRACE_EVENT1(TRACE_DISABLED_BY_DEFAULT("devtools.timeline"), "ScrollLayer", "data", InspectorScrollLayerEvent::data(&box()));
     // FIXME(361045): remove InspectorInstrumentation calls once DevTools Timeline migrates to tracing.
     InspectorInstrumentation::willScrollLayer(&box());
 
     const RenderLayerModelObject* paintInvalidationContainer = box().containerForPaintInvalidation();
 
     // Update the positions of our child layers (if needed as only fixed layers should be impacted by a scroll).
     // We don't update compositing layers, because we need to do a deep update from the compositing ancestor.
     if (!frameView->isInPerformLayout()) {
@@ skipping 471 matching lines @@
     if (Node* node = renderer.node()) {
         if (ShadowRoot* shadowRoot = node->containingShadowRoot()) {
             if (shadowRoot->type() == ShadowRoot::UserAgentShadowRoot)
                 return shadowRoot->host()->renderer();
         }
     }
 
     return &renderer;
 }
 
-PassRefPtr<Scrollbar> RenderLayerScrollableArea::createScrollbar(ScrollbarOrientation orientation)
+PassRefPtrWillBeRawPtr<Scrollbar> RenderLayerScrollableArea::createScrollbar(ScrollbarOrientation orientation)
 {
-    RefPtr<Scrollbar> widget;
+    RefPtrWillBeRawPtr<Scrollbar> widget = nullptr;
     RenderObject* actualRenderer = rendererForScrollbar(box());
     bool hasCustomScrollbarStyle = actualRenderer->isBox() && actualRenderer->style()->hasPseudoStyle(SCROLLBAR);
     if (hasCustomScrollbarStyle) {
         widget = RenderScrollbar::createCustomScrollbar(this, orientation, actualRenderer->node());
     } else {
         ScrollbarControlSize scrollbarSize = RegularScrollbar;
         if (actualRenderer->style()->hasAppearance())
             scrollbarSize = RenderTheme::theme().scrollbarControlSizeForPart(actualRenderer->style()->appearance());
         widget = Scrollbar::create(this, orientation, scrollbarSize);
         if (orientation == HorizontalScrollbar)
             didAddScrollbar(widget.get(), HorizontalScrollbar);
         else
             didAddScrollbar(widget.get(), VerticalScrollbar);
     }
     box().document().view()->addChild(widget.get());
     return widget.release();
 }
 
 void RenderLayerScrollableArea::destroyScrollbar(ScrollbarOrientation orientation)
 {
-    RefPtr<Scrollbar>& scrollbar = orientation == HorizontalScrollbar ? m_hBar : m_vBar;
+    RefPtrWillBePersistent<Scrollbar>& scrollbar = orientation == HorizontalScrollbar ? m_hBar : m_vBar;
     if (!scrollbar)
         return;
 
     if (!scrollbar->isCustomScrollbar())
         willRemoveScrollbar(scrollbar.get(), orientation);
 
     toScrollView(scrollbar->parent())->removeChild(scrollbar.get());
     scrollbar->disconnectFromScrollableArea();
     scrollbar = nullptr;
 }
@@ skipping 583 matching lines @@
 void RenderLayerScrollableArea::setTopmostScrollChild(RenderLayer* scrollChild)
 {
     // We only want to track the topmost scroll child for scrollable areas with
     // overlay scrollbars.
     if (!hasOverlayScrollbars())
         return;
     m_nextTopmostScrollChild = scrollChild;
 }
 
 } // namespace blink