Introduce previousPositionOf() for VisiblePosition

Source/core/editing/commands/InsertParagraphSeparatorCommand.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 248 matching lines @@
         appendBlockPlaceholder(parent);
 
         setEndingSelection(VisibleSelection(firstPositionInNode(parent.get()), TextAffinity::Downstream, endingSelection().isDirectional()));
         return;
     }
 
 
     //---------------------------------------------------------------------
     // Handle case when position is in the first visible position in its block, and
     // similar case where previous position is in another, presumeably nested, block.
-    if (isFirstInBlock || !inSameBlock(visiblePos, visiblePos.previous())) {
+    if (isFirstInBlock || !inSameBlock(visiblePos, previousPositionOf(visiblePos))) {
         Node* refNode = nullptr;
         insertionPosition = positionOutsideTabSpan(insertionPosition);
 
         if (isFirstInBlock && !nestNewBlock) {
             if (listChild && listChild != startBlock) {
                 RefPtrWillBeRawPtr<Element> listChildToInsert = listChild->cloneElementWithoutChildren();
                 appendNode(blockToInsert, listChildToInsert.get());
                 insertNodeBefore(listChildToInsert.get(), listChild);
             } else {
                 refNode = startBlock.get();
@@ skipping 153 matching lines @@
 }
 
 DEFINE_TRACE(InsertParagraphSeparatorCommand)
 {
     visitor->trace(m_style);
     CompositeEditCommand::trace(visitor);
 }
 
 
 } // namespace blink