Allow assertions to be enabled in Blink Release builds.

Source/core/editing/VisiblePosition.cpp

 /*
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009 Apple Inc. All rights reserved.
  * Portions Copyright (c) 2011 Motorola Mobility, 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 78 matching lines @@
 {
     Position pos = previousVisuallyDistinctCandidate(m_deepPosition);
 
     // return null visible position if there is no previous visible position
     if (pos.atStartOfTree())
         return VisiblePosition();
 
     VisiblePosition prev = VisiblePosition(pos, DOWNSTREAM);
     ASSERT(prev != *this);
 
-#ifndef NDEBUG
+#if ENABLE(ASSERT)
     // we should always be able to make the affinity DOWNSTREAM, because going previous from an
     // UPSTREAM position can never yield another UPSTREAM position (unless line wrap length is 0!).
     if (prev.isNotNull() && m_affinity == UPSTREAM) {
         VisiblePosition temp = prev;
         temp.setAffinity(UPSTREAM);
         ASSERT(inSameLine(temp, prev));
     }
 #endif
 
     switch (rule) {
@@ skipping 694 matching lines @@
     if (vpos)
         vpos->showTreeForThis();
 }
 
 void showTree(const WebCore::VisiblePosition& vpos)
 {
     vpos.showTreeForThis();
 }
 
 #endif