Allocate OverlapMapContainers in vector rather than on stack with copy

third_party/WebKit/Source/core/layout/compositing/CompositingRequirementsUpdater.cpp

 /*
  * Copyright (C) 2009, 2010 Apple Inc. All rights reserved.
  * Copyright (C) 2014 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
@@ skipping 100 matching lines @@
       return clippedOverlap;
     // Unclipped is allowed to overlap clipped, but not vice-versa.
     return clippedOverlap ||
            m_overlapStack.last().unclipped.overlapsLayers(bounds);
   }
 
   void beginNewOverlapTestingContext() {
     // This effectively creates a new "clean slate" for overlap state.
     // This is used when we know that a subtree or remaining set of
     // siblings does not need to check overlap with things behind it.
-    m_overlapStack.append(OverlapMapContainers());
+    m_overlapStack.grow(m_overlapStack.size() + 1);
   }
 
   void finishCurrentOverlapTestingContext() {
     // The overlap information on the top of the stack is still necessary
     // for checking overlap of any layers outside this context that may
     // overlap things from inside this context. Therefore, we must merge
     // the information from the top of the stack before popping the stack.
     //
     // FIXME: we may be able to avoid this deep copy by rearranging how
     //        overlapMap state is managed.
@@ skipping 406 matching lines @@
     descendantHas3DTransform |=
         anyDescendantHas3DTransform || layer->has3DTransform();
   }
 
   // At this point we have finished collecting all reasons to composite this
   // layer.
   layer->setCompositingReasons(reasonsToComposite);
 }
 
 }  // namespace blink