[Editing][CodeHealth] Move Position::up/downstream implementation to VisibleUnit.cpp

Source/core/editing/VisibleUnits.h

 /*
  * Copyright (C) 2004 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 25 matching lines @@
 class LayoutRect;
 class LayoutUnit;
 class LayoutObject;
 class Node;
 class VisiblePosition;
 class IntPoint;
 class LocalFrame;
 
 enum EWordSide { RightWordIfOnBoundary = false, LeftWordIfOnBoundary = true };
 
+// Position
+// mostForward/BackwardCaretPosition are used for moving back and forth between
+// visually equivalent candidates.
+// For example, for the text node "foo     bar" where whitespace is
+// collapsible, there are two candidates that map to the VisiblePosition
+// between 'b' and the space, after first space and before last space.
+//
+// mostForwardCaretPosition returns the left candidate and also returs
+// [boundary, 0] for any of the positions from [boundary, 0] to the first
+// candidate in boundary, where
+// endsOfNodeAreVisuallyDistinctPositions(boundary) is true.
+//
+// mostBackwardCaretPosition() returns the right one and also returns the
+// last position in the last atomic node in boundary for all of the positions
+// in boundary after the last candidate, where
+// endsOfNodeAreVisuallyDistinctPositions(boundary).
+// FIXME: This function should never be called when the line box tree is dirty.
+// See https://bugs.webkit.org/show_bug.cgi?id=97264
+CORE_EXPORT Position mostForwardCaretPosition(const Position &, EditingBoundaryCrossingRule = CannotCrossEditingBoundary);
+CORE_EXPORT PositionInComposedTree mostForwardCaretPosition(const PositionInComposedTree &, EditingBoundaryCrossingRule = CannotCrossEditingBoundary);
+CORE_EXPORT Position mostBackwardCaretPosition(const Position &, EditingBoundaryCrossingRule = CannotCrossEditingBoundary);
+CORE_EXPORT PositionInComposedTree mostBackwardCaretPosition(const PositionInComposedTree &, EditingBoundaryCrossingRule = CannotCrossEditingBoundary);
+
 // words
 CORE_EXPORT VisiblePosition startOfWord(const VisiblePosition &, EWordSide = RightWordIfOnBoundary);
 CORE_EXPORT VisiblePosition endOfWord(const VisiblePosition &, EWordSide = RightWordIfOnBoundary);
 VisiblePosition previousWordPosition(const VisiblePosition &);
 VisiblePosition nextWordPosition(const VisiblePosition &);
 VisiblePosition rightWordPosition(const VisiblePosition&, bool skipsSpaceWhenMovingRight);
 VisiblePosition leftWordPosition(const VisiblePosition&, bool skipsSpaceWhenMovingRight);
 
 // sentences
 CORE_EXPORT VisiblePosition startOfSentence(const VisiblePosition &);
@@ skipping 52 matching lines @@
 
 // Returns a hit-tested VisiblePosition for the given point in contents-space
 // coordinates.
 CORE_EXPORT VisiblePosition visiblePositionForContentsPoint(const IntPoint&, LocalFrame*);
 
 CORE_EXPORT bool rendersInDifferentPosition(const Position&, const Position&);
 
 } // namespace blink
 
 #endif // VisibleUnits_h