Only not take zOffset into account during hit-testing when child layers are in the same 3d renderin…

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 2840 matching lines @@
     double localZOffset = -numeric_limits<double>::infinity();
     double* zOffsetForDescendantsPtr = 0;
     double* zOffsetForContentsPtr = 0;
 
     bool depthSortDescendants = false;
     if (preserves3D()) {
         depthSortDescendants = true;
         // Our layers can depth-test with our container, so share the z depth pointer with the container, if it passed one down.
         zOffsetForDescendantsPtr = zOffset ? zOffset : &localZOffset;
         zOffsetForContentsPtr = zOffset ? zOffset : &localZOffset;
-    } else if (m_has3DTransformedDescendant) {
-        // Flattening layer with 3d children; use a local zOffset pointer to depth-test children and foreground.
-        depthSortDescendants = true;
-        zOffsetForDescendantsPtr = zOffset ? zOffset : &localZOffset;
-        zOffsetForContentsPtr = zOffset ? zOffset : &localZOffset;
     } else if (zOffset) {
         zOffsetForDescendantsPtr = 0;
         // Container needs us to give back a z offset for the hit layer.
         zOffsetForContentsPtr = zOffset;
     }
 
     // This variable tracks which layer the mouse ends up being inside.
     RenderLayer* candidateLayer = 0;
 
     // Begin by walking our list of positive layers from highest z-index down to the lowest z-index.
@@ skipping 1210 matching lines @@
     }
 }
 
 void showLayerTree(const WebCore::RenderObject* renderer)
 {
     if (!renderer)
         return;
     showLayerTree(renderer->enclosingLayer());
 }
 #endif