Oilpan: improve ScrollableArea handling.

Source/core/paint/DeprecatedPaintLayerScrollableArea.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 72 matching lines @@
     : m_layer(layer)
     , m_inResizeMode(false)
     , m_scrollsOverflow(false)
     , m_scrollDimensionsDirty(true)
     , m_inOverflowRelayout(false)
     , m_nextTopmostScrollChild(0)
     , m_topmostScrollChild(0)
     , m_needsCompositedScrolling(false)
     , m_scrollCorner(nullptr)
     , m_resizer(nullptr)
+#if ENABLE(ASSERT)
+    , m_hasBeenDisposed(false)
+#endif
 {
     Node* node = box().node();
     if (node && node->isElementNode()) {
         // We save and restore only the scrollOffset as the other scroll values are recalculated.
         Element* element = toElement(node);
         m_scrollOffset = element->savedLayerScrollOffset();
         if (!m_scrollOffset.isZero())
             scrollAnimator()->setCurrentPosition(FloatPoint(m_scrollOffset.width(), m_scrollOffset.height()));
         element->setSavedLayerScrollOffset(IntSize());
     }
 
     updateResizerAreaSet();
 }
 
 DeprecatedPaintLayerScrollableArea::~DeprecatedPaintLayerScrollableArea()
 {
+    ASSERT(m_hasBeenDisposed);
+}
+
+void DeprecatedPaintLayerScrollableArea::dispose()
+{
     if (inResizeMode() && !box().documentBeingDestroyed()) {
         if (LocalFrame* frame = box().frame())
             frame->eventHandler().resizeScrollableAreaDestroyed();
     }
 
     if (LocalFrame* frame = box().frame()) {
         if (FrameView* frameView = frame->view()) {
             frameView->removeScrollableArea(this);
             frameView->removeAnimatingScrollableArea(this);
         }
@@ skipping 16 matching lines @@
             frameView->removeResizerArea(box());
     }
 
     destroyScrollbar(HorizontalScrollbar);
     destroyScrollbar(VerticalScrollbar);
 
     if (m_scrollCorner)
         m_scrollCorner->destroy();
     if (m_resizer)
         m_resizer->destroy();
+
+#if ENABLE(ASSERT)
+    m_hasBeenDisposed = true;
+#endif
+}
+
+DEFINE_TRACE(DeprecatedPaintLayerScrollableArea)
+{
+    visitor->trace(m_hBar);
+    visitor->trace(m_vBar);
+    ScrollableArea::trace(visitor);
 }
 
 HostWindow* DeprecatedPaintLayerScrollableArea::hostWindow() const
 {
     if (Page* page = box().frame()->page())
         return &page->chromeClient();
     return nullptr;
 }
 
 GraphicsLayer* DeprecatedPaintLayerScrollableArea::layerForScrolling() const
@@ skipping 773 matching lines @@
             didAddScrollbar(widget.get(), HorizontalScrollbar);
         else
             didAddScrollbar(widget.get(), VerticalScrollbar);
     }
     box().document().view()->addChild(widget.get());
     return widget.release();
 }
 
 void DeprecatedPaintLayerScrollableArea::destroyScrollbar(ScrollbarOrientation orientation)
 {
-    RefPtrWillBePersistent<Scrollbar>& scrollbar = orientation == HorizontalScrollbar ? m_hBar : m_vBar;
+    RefPtrWillBeMember<Scrollbar>& scrollbar = orientation == HorizontalScrollbar ? m_hBar : m_vBar;
     if (!scrollbar)
         return;
 
     if (!scrollbar->isCustomScrollbar())
         willRemoveScrollbar(scrollbar.get(), orientation);
 
     toFrameView(scrollbar->parent())->removeChild(scrollbar.get());
     scrollbar->disconnectFromScrollableArea();
     scrollbar = nullptr;
 }
@@ skipping 444 matching lines @@
 void DeprecatedPaintLayerScrollableArea::setTopmostScrollChild(DeprecatedPaintLayer* scrollChild)
 {
     // We only want to track the topmost scroll child for scrollable areas with
     // overlay scrollbars.
     if (!hasOverlayScrollbars())
         return;
     m_nextTopmostScrollChild = scrollChild;
 }
 
 } // namespace blink