Fix chicken and egg problem in composited bounds computation

Source/core/rendering/RenderLayer.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 3582 matching lines @@
 
 #if !ASSERT_DISABLED
     LayerListMutationDetector mutationChecker(const_cast<RenderLayer*>(this)->stackingNode());
 #endif
 
     // FIXME: Descendants that are composited should not necessarily be skipped, if they don't paint into their own
     // separate backing. Instead, they ought to contribute to the bounds of the layer we're trying to compute.
     // This applies to all z-order lists below.
     RenderLayerStackingNodeIterator iterator(*m_stackingNode.get(), AllChildren);
     while (RenderLayerStackingNode* node = iterator.next()) {
+        // Node's compositing ancestor may have changed its draw content status
+        // prior to updating its bounds. The requires-own-backing-store-for-ancestor-reasons
+        // could be stale. Refresh them now.
+        if (node->layer()->hasCompositedLayerMapping()) {
+            RenderLayer* enclosingCompositingLayer = node->layer()->enclosingCompositingLayer(false);
+            node->layer()->compositedLayerMapping()->updateRequiresOwnBackingStoreForAncestorReasons(enclosingCompositingLayer);
+        }
+
         if (flags & IncludeCompositedDescendants || !node->layer()->hasCompositedLayerMapping()) {
             IntRect childUnionBounds = node->layer()->calculateLayerBounds(this, 0, descendantFlags);
             unionBounds.unite(childUnionBounds);
         }
     }
 
     // FIXME: We can optimize the size of the composited layers, by not enlarging
     // filtered areas with the outsets if we know that the filter is going to render in hardware.
     // https://bugs.webkit.org/show_bug.cgi?id=81239
     if (flags & IncludeLayerFilterOutsets)
@@ skipping 544 matching lines @@
     }
 }
 
 void showLayerTree(const WebCore::RenderObject* renderer)
 {
     if (!renderer)
         return;
     showLayerTree(renderer->enclosingLayer());
 }
 #endif