Introduce previousPositionOf() for VisiblePosition

Source/core/editing/Editor.cpp

 /*
  * Copyright (C) 2006, 2007, 2008, 2011 Apple Inc. All rights reserved.
  * Copyright (C) 2008 Nokia Corporation and/or its subsidiary(-ies)
  *
  * 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 238 matching lines @@
     Node* startContainer = range.startPosition().computeContainerNode();
     Node* endContainer = range.endPosition().computeContainerNode();
     if (!startContainer || !endContainer)
         return false;
 
     if (!startContainer->hasEditableStyle() || !endContainer->hasEditableStyle())
         return false;
 
     if (range.isCollapsed()) {
         VisiblePosition start(range.startPosition());
-        VisiblePosition previous = start.previous();
+        VisiblePosition previous = previousPositionOf(start);
         // FIXME: We sometimes allow deletions at the start of editable roots, like when the caret is in an empty list item.
         if (previous.isNull() || previous.deepEquivalent().anchorNode()->rootEditableElement() != startContainer->rootEditableElement())
             return false;
     }
     return true;
 }
 
 bool Editor::smartInsertDeleteEnabled() const
 {
     if (Settings* settings = frame().settings())
@@ skipping 747 matching lines @@
     if (!canEdit())
         return;
 
     VisibleSelection selection = frame().selection().selection();
     if (!selection.isCaret())
         return;
 
     // Make a selection that goes back one character and forward two characters.
     VisiblePosition caret = selection.visibleStart();
     VisiblePosition next = isEndOfParagraph(caret) ? caret : caret.next();
-    VisiblePosition previous = next.previous();
+    VisiblePosition previous = previousPositionOf(next);
     if (next.deepEquivalent() == previous.deepEquivalent())
         return;
-    previous = previous.previous();
+    previous = previousPositionOf(previous);
     if (!inSameParagraph(next, previous))
         return;
     const EphemeralRange range = makeRange(previous, next);
     if (range.isNull())
         return;
     VisibleSelection newSelection(range);
 
     // Transpose the two characters.
     String text = plainText(range);
     if (text.length() != 2)
@@ skipping 260 matching lines @@
 }
 
 DEFINE_TRACE(Editor)
 {
     visitor->trace(m_frame);
     visitor->trace(m_lastEditCommand);
     visitor->trace(m_mark);
 }
 
 } // namespace blink