Remove unnecessary layout updates from InsertInto/DeleteFromTextNodeCommand

third_party/WebKit/Source/core/editing/commands/InsertLineBreakCommand.cpp

 /*
  * Copyright (C) 2005, 2006 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 159 matching lines @@
     Position endingPosition = Position::firstPositionInNode(textNode);
 
     // Handle whitespace that occurs after the split
     document().updateStyleAndLayoutIgnorePendingStylesheets();
     // TODO(yosin) |isRenderedCharacter()| should be removed, and we should
     // use |VisiblePosition::characterAfter()|.
     if (!isRenderedCharacter(endingPosition)) {
       Position positionBeforeTextNode(Position::inParentBeforeNode(*textNode));
       // Clear out all whitespace and insert one non-breaking space
       deleteInsignificantTextDownstream(endingPosition);
-      DCHECK(!textNode->layoutObject() ||

[yosin_UTC9, 2017/02/22 06:26:08]

I really don't like this DCHECK() since it depends on how layout produces and
layering violation.
Also, we don't need to have this kind of DCHECK() here. Rather, we should have
unit test for 
|deleteInsignificantTextDownstream()|. (I don't ask you to write it)

-             textNode->layoutObject()->style()->collapseWhiteSpace());
       // Deleting insignificant whitespace will remove textNode if it contains
       // nothing but insignificant whitespace.
       if (textNode->isConnected()) {
         insertTextIntoNode(textNode, 0, nonBreakingSpaceString());
       } else {
         Text* nbspNode = document().createTextNode(nonBreakingSpaceString());
         insertNodeAt(nbspNode, positionBeforeTextNode, editingState);
         if (editingState->isAborted())
           return;
         endingPosition = Position::firstPositionInNode(nbspNode);
@@ skipping 31 matching lines @@
     // block.
     setEndingSelection(SelectionInDOMTree::Builder()
                            .collapse(endingSelection().end())
                            .build());
   }
 
   rebalanceWhitespace();
 }
 
 }  // namespace blink