Move {next,previous}PositionOf() for VisiblePosition to VisibleUnits.cpp

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 f2099ab571f0bd4186f87021f692fab9a51f61a4..7d6f4cb97c7390a41a4afa690768f77e59ff6344 100644
--- a/Source/core/editing/VisiblePosition.h
+++ b/Source/core/editing/VisiblePosition.h
@@ -27,11 +27,9 @@
 #define VisiblePosition_h
 
 #include "core/CoreExport.h"
-#include "core/editing/EditingBoundary.h"
 #include "core/editing/PositionWithAffinity.h"
 #include "core/editing/TextAffinity.h"
 #include "platform/heap/Handle.h"
-#include "platform/text/TextDirection.h"
 
 namespace blink {
 
@@ -147,11 +145,6 @@ PositionWithAffinity honorEditingBoundaryAtOrBeforeOf(const PositionWithAffinity
 PositionInComposedTreeWithAffinity honorEditingBoundaryAtOrBeforeOf(const PositionInComposedTreeWithAffinity&, const PositionInComposedTree& anchor);
 VisiblePosition honorEditingBoundaryAtOrAfter(const VisiblePosition&, const Position& anchor);
 
-// TODO(yosin) We should move |nextPositionOf()| to "VisibleUnits.cpp".
-VisiblePosition nextPositionOf(const VisiblePosition&, EditingBoundaryCrossingRule = CanCrossEditingBoundary);
-// TODO(yosin) We should move |previousPositionOf()| to "VisibleUnits.cpp"
-VisiblePosition previousPositionOf(const VisiblePosition&, EditingBoundaryCrossingRule = CanCrossEditingBoundary);
-
 CORE_EXPORT VisiblePosition visiblePositionOf(const Position&, TextAffinity = VP_DEFAULT_AFFINITY);
 CORE_EXPORT VisiblePosition visiblePositionOf(const PositionInComposedTree&, TextAffinity = VP_DEFAULT_AFFINITY);