Have positionInParentBeforeNode() / positionInParentAfterNode() take a reference

Source/core/editing/InsertTextCommand.cpp

 /*
  * Copyright (C) 2005 Apple Computer, 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
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 146 matching lines @@
         // Don't remove the placeholder yet, otherwise the block we're inserting into would collapse before
         // we get a chance to insert into it.  We check for a placeholder now, though, because doing so requires
         // the creation of a VisiblePosition, and if we did that post-insertion it would force a layout.
     }
 
     // Insert the character at the leftmost candidate.
     startPosition = startPosition.upstream();
 
     // It is possible for the node that contains startPosition to contain only unrendered whitespace,
     // and so deleteInsignificantText could remove it.  Save the position before the node in case that happens.
-    Position positionBeforeStartNode(positionInParentBeforeNode(startPosition.containerNode()));
+    ASSERT(startPosition.containerNode());
+    Position positionBeforeStartNode(positionInParentBeforeNode(*startPosition.containerNode()));
     deleteInsignificantText(startPosition, startPosition.downstream());
     if (!startPosition.inDocument())
         startPosition = positionBeforeStartNode;
     if (!startPosition.isCandidate())
         startPosition = startPosition.downstream();
 
     startPosition = positionAvoidingSpecialElementBoundary(startPosition);
 
     Position endPosition;
 
@@ skipping 75 matching lines @@
                 splitTextNode(textNode, offset);
             insertNodeBefore(spanNode, textNode.release());
         }
     }
 
     // return the position following the new tab
     return lastPositionInNode(spanNode.get());
 }
 
 }