Oilpan: improve ScrollableArea handling.

Source/core/paint/DeprecatedPaintLayer.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 131 matching lines @@
     m_isSelfPaintingLayer = shouldBeSelfPaintingLayer();
 
     if (!layoutObject->slowFirstChild() && layoutObject->style()) {
         m_visibleContentStatusDirty = false;
         m_hasVisibleContent = layoutObject->style()->visibility() == VISIBLE;
     }
 
     updateScrollableArea();
 }
 
 DeprecatedPaintLayer::~DeprecatedPaintLayer()

[haraken, 2015/06/29 15:20:21]

DeprecatedPaintLayer is explicitly destructed in
LayoutBoxModelObject::destroyLayer. I'd prefer introducing
DeprecatedPaintLayer::dispose and move the contents of ~DeprecatedPaintLayer()
into the dispose method. It will make it clearer that we're not relying on
destructors.

[sof, 2015/06/29 15:59:41]

How is that related to Oilpan? DeprecatedPaintLayer is not on the heap.

 {
     if (layoutObject()->frame() && layoutObject()->frame()->page()) {
         if (ScrollingCoordinator* scrollingCoordinator = layoutObject()->frame()->page()->scrollingCoordinator())
             scrollingCoordinator->willDestroyLayer(this);
     }
 
     removeFilterInfoIfNeeded();
 
     if (groupedMapping()) {
         DisableCompositingQueryAsserts disabler;
         groupedMapping()->removeLayerFromSquashingGraphicsLayer(this);
         setGroupedMapping(0);
     }
 
     // Child layers will be deleted by their corresponding layout objects, so
     // we don't need to delete them ourselves.
 
     clearCompositedDeprecatedPaintLayerMapping(true);
 
     if (m_reflectionInfo)
         m_reflectionInfo->destroy();
+
+    if (m_scrollableArea)
+        m_scrollableArea->dispose();
 }
 
 String DeprecatedPaintLayer::debugName() const
 {
     if (isReflection())
         return layoutObject()->parent()->debugName() + " (reflection)";
     return layoutObject()->debugName();
 }
 
 DeprecatedPaintLayerCompositor* DeprecatedPaintLayer::compositor() const
@@ skipping 1251 matching lines @@
 {
     if (requiresStackingNode())
         m_stackingNode = adoptPtr(new DeprecatedPaintLayerStackingNode(*layoutObject()));
     else
         m_stackingNode = nullptr;
 }
 
 void DeprecatedPaintLayer::updateScrollableArea()
 {
     if (requiresScrollableArea())
-        m_scrollableArea = adoptPtr(new DeprecatedPaintLayerScrollableArea(*this));
+        m_scrollableArea = DeprecatedPaintLayerScrollableArea::create(*this);
     else
         m_scrollableArea = nullptr;

[haraken, 2015/06/29 15:20:21]

Don't we need to call m_scrollableArea->dispose() here?

[sof, 2015/06/29 15:59:41]

I'm not familiar with the naming for this helper, but it's only called from the
constructor.

 }
 
 bool DeprecatedPaintLayer::hasOverflowControls() const
 {
     return m_scrollableArea && (m_scrollableArea->hasScrollbar() || m_scrollableArea->scrollCorner() || layoutObject()->style()->resize() != RESIZE_NONE);
 }
 
 void DeprecatedPaintLayer::appendSingleFragmentIgnoringPagination(DeprecatedPaintLayerFragments& fragments, const DeprecatedPaintLayer* rootLayer, const LayoutRect& dirtyRect, ClipRectsCacheSlot clipRectsCacheSlot, OverlayScrollbarSizeRelevancy inOverlayScrollbarSizeRelevancy, ShouldRespectOverflowClip respectOverflowClip, const LayoutPoint* offsetFromRoot, const LayoutSize& subPixelAccumulation)
 {
     DeprecatedPaintLayerFragment fragment;
@@ skipping 1278 matching lines @@
 
 void showLayerTree(const blink::LayoutObject* layoutObject)
 {
     if (!layoutObject) {
         fprintf(stderr, "Cannot showLayerTree. Root is (nil)\n");
         return;
     }
     showLayerTree(layoutObject->enclosingLayer());
 }
 #endif