Introduce previousPositionOf() for VisiblePosition

Source/core/editing/VisiblePosition.h

Index: Source/core/editing/VisiblePosition.h
diff --git a/Source/core/editing/VisiblePosition.h b/Source/core/editing/VisiblePosition.h
index 405202bf5a05e75eed0d389c8184713dc6f8fe14..780b1302e40fe4329228fa4511aa614eda1df1b0 100644
--- a/Source/core/editing/VisiblePosition.h
+++ b/Source/core/editing/VisiblePosition.h
@@ -96,7 +96,6 @@ public:
 
     // next() and previous() will increment/decrement by a character cluster.
     VisiblePosition next(EditingBoundaryCrossingRule = CanCrossEditingBoundary) const;
-    VisiblePosition previous(EditingBoundaryCrossingRule = CanCrossEditingBoundary) const;
     VisiblePosition honorEditingBoundaryAtOrBefore(const VisiblePosition&) const;
     VisiblePosition honorEditingBoundaryAtOrAfter(const VisiblePosition&) const;
     VisiblePosition skipToStartOfEditingBoundary(const VisiblePosition&) const;
@@ -106,7 +105,7 @@ public:
     VisiblePosition right() const;
 
     UChar32 characterAfter() const;
-    UChar32 characterBefore() const { return previous().characterAfter(); }
+    UChar32 characterBefore() const;
 
     // FIXME: This does not handle [table, 0] correctly.
     Element* rootEditableElement() const { return m_deepPosition.isNotNull() ? m_deepPosition.anchorNode()->rootEditableElement() : 0; }
@@ -145,6 +144,9 @@ CORE_EXPORT PositionInComposedTree canonicalPositionOf(const PositionInComposedT
 PositionWithAffinity honorEditingBoundaryAtOrBeforeOf(const PositionWithAffinity&, const Position& anchor);
 PositionInComposedTreeWithAffinity honorEditingBoundaryAtOrBeforeOf(const PositionInComposedTreeWithAffinity&, const PositionInComposedTree& anchor);
 
+// TODO(yosin) We should move |previousPositionOf()| to "VisibleUnits.cpp"
+VisiblePosition previousPositionOf(const VisiblePosition&, EditingBoundaryCrossingRule = CanCrossEditingBoundary);
+
 } // namespace blink
 
 #ifndef NDEBUG