Introduce previousPositionOf() for VisiblePosition

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 62 matching lines @@
         return next;
     case CannotCrossEditingBoundary:
         return honorEditingBoundaryAtOrAfter(next);
     case CanSkipOverEditingBoundary:
         return skipToEndOfEditingBoundary(next);
     }
     ASSERT_NOT_REACHED();
     return honorEditingBoundaryAtOrAfter(next);
 }
 
-VisiblePosition VisiblePosition::previous(EditingBoundaryCrossingRule rule) const
+VisiblePosition previousPositionOf(const VisiblePosition& visiblePosition, EditingBoundaryCrossingRule rule)
 {
-    Position pos = previousVisuallyDistinctCandidate(m_deepPosition);
+    Position pos = previousVisuallyDistinctCandidate(visiblePosition.deepEquivalent());
 
     // return null visible position if there is no previous visible position
     if (pos.atStartOfTree())
         return VisiblePosition();
 
     VisiblePosition prev = VisiblePosition(pos);
-    ASSERT(prev.deepEquivalent() != m_deepPosition);
+    ASSERT(prev.deepEquivalent() != visiblePosition.deepEquivalent());
 
 #if ENABLE(ASSERT)
     // we should always be able to make the affinity |TextAffinity::Downstream|,
     // because going previous from an |TextAffinity::Upstream| position can
     // never yield another |TextAffinity::Upstream position| (unless line wrap
     // length is 0!).
-    if (prev.isNotNull() && m_affinity == TextAffinity::Upstream) {
+    if (prev.isNotNull() && visiblePosition.affinity() == TextAffinity::Upstream) {
         ASSERT(inSameLine(PositionWithAffinity(prev.deepEquivalent()), PositionWithAffinity(prev.deepEquivalent(), TextAffinity::Upstream)));
     }
 #endif
 
     switch (rule) {
     case CanCrossEditingBoundary:
         return prev;
     case CannotCrossEditingBoundary:
-        return honorEditingBoundaryAtOrBefore(prev);
+        return visiblePosition.honorEditingBoundaryAtOrBefore(prev);
     case CanSkipOverEditingBoundary:
-        return skipToStartOfEditingBoundary(prev);
+        return visiblePosition.skipToStartOfEditingBoundary(prev);
     }
 
     ASSERT_NOT_REACHED();
-    return honorEditingBoundaryAtOrBefore(prev);
+    return visiblePosition.honorEditingBoundaryAtOrBefore(prev);
 }
 
 Position VisiblePosition::leftVisuallyDistinctCandidate() const
 {
     Position p = m_deepPosition;
     if (p.isNull())
         return Position();
 
     Position downstreamStart = mostForwardCaretPosition(p);
     TextDirection primaryDirection = primaryDirectionOf(*p.anchorNode());
@@ skipping 549 matching lines @@
         return 0;
     unsigned offset = static_cast<unsigned>(pos.offsetInContainerNode());
     Text* textNode = toText(containerNode);
     unsigned length = textNode->length();
     if (offset >= length)
         return 0;
 
     return textNode->data().characterStartingAt(offset);
 }
 
+UChar32 VisiblePosition::characterBefore() const
+{
+    return previousPositionOf(*this).characterAfter();
+}
+
 LayoutRect VisiblePosition::localCaretRect(LayoutObject*& layoutObject) const
 {
     PositionWithAffinity positionWithAffinity(m_deepPosition, m_affinity);
     return localCaretRectOfPosition(positionWithAffinity, layoutObject);
 }
 
 IntRect VisiblePosition::absoluteCaretBounds() const
 {
     LayoutObject* layoutObject;
     LayoutRect localRect = localCaretRect(layoutObject);
@@ skipping 75 matching lines @@
     else
         fprintf(stderr, "Cannot showTree for (nil) VisiblePosition.\n");
 }
 
 void showTree(const blink::VisiblePosition& vpos)
 {
     vpos.showTreeForThis();
 }
 
 #endif