Add clean layout DCHECK to mostBackwardCaretPosition()

third_party/WebKit/Source/core/editing/VisibleUnits.cpp

 /*
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009 Apple 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 2826 matching lines @@
   if (isAtomicNode(pos.node()))
     return true;
 
   return pos.atStartOfNode();
 }
 
 template <typename Strategy>
 static PositionTemplate<Strategy> mostBackwardCaretPosition(
     const PositionTemplate<Strategy>& position,
     EditingBoundaryCrossingRule rule) {
+  DCHECK(!needsLayoutTreeUpdate(position)) << position;
   TRACE_EVENT0("input", "VisibleUnits::mostBackwardCaretPosition");
 
   Node* startNode = position.anchorNode();
   if (!startNode)
     return PositionTemplate<Strategy>();
 
   // iterate backward from there, looking for a qualified position
   Node* boundary = enclosingVisualBoundary<Strategy>(startNode);
   // FIXME: PositionIterator should respect Before and After positions.
   PositionIteratorAlgorithm<Strategy> lastVisible(
@@ skipping 1073 matching lines @@
 
 VisiblePositionInFlatTree previousPositionOf(
     const VisiblePositionInFlatTree& visiblePosition,
     EditingBoundaryCrossingRule rule) {
   DCHECK(visiblePosition.isValid()) << visiblePosition;
   return previousPositionOfAlgorithm<EditingInFlatTreeStrategy>(
       visiblePosition.deepEquivalent(), rule);
 }
 
 }  // namespace blink