Defer call to updateWidgetPositions() outside of RenderLayerScrollableArea.

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 348 matching lines @@
     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()) {
         // If we're in the middle of layout, we'll just update layers once layout has finished.
         layer()->clipper().clearClipRectsIncludingDescendants();
         box().setPreviousPaintInvalidationRect(box().boundsRectForPaintInvalidation(paintInvalidationContainer));
         // Update regions, scrolling may change the clip of a particular region.
         frameView->updateAnnotatedRegions();
-        // FIXME: We shouldn't call updateWidgetPositions() here since it might tear down the render tree,
-        // for now we just crash to avoid allowing an attacker to use after free.
-        frameView->updateWidgetPositions();
-        RELEASE_ASSERT(frameView->renderView());

[hartmanng, 2014/08/20 15:33:10]

I don't think this RELEASE_ASSERT is necessary anymore - it was added to try to
deal with this use-after-free (see https://codereview.chromium.org/132913002 and
the deleted comment above)

+        frameView->setNeedsUpdateWidgetPositions();
         updateCompositingLayersAfterScroll();
     }
 
     // The caret rect needs to be invalidated after scrolling
     frame->selection().setCaretRectNeedsUpdate();
 
     FloatQuad quadForFakeMouseMoveEvent = FloatQuad(layer()->renderer()->previousPaintInvalidationRect());
 
     quadForFakeMouseMoveEvent = paintInvalidationContainer->localToAbsoluteQuad(quadForFakeMouseMoveEvent);
     frame->eventHandler().dispatchFakeMouseMoveEventSoonInQuad(quadForFakeMouseMoveEvent);
@@ skipping 1085 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