Move computeInlineBoxPosition() to VisibleUnits.{cpp,h} from Position.{cpp,h} and VisiblePosition.h

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 05d691b0089e2c19a7add6f5556a8470ccef3d7a..405202bf5a05e75eed0d389c8184713dc6f8fe14 100644
--- a/Source/core/editing/VisiblePosition.h
+++ b/Source/core/editing/VisiblePosition.h
@@ -138,13 +138,6 @@ private:
     TextAffinity m_affinity;
 };
 
-// TODO(yosin) We should move |computeInlineBoxPosition()| to "VisibleUnits.h"
-// with |Position| version.
-inline InlineBoxPosition computeInlineBoxPosition(const VisiblePosition& position)
-{
-    return computeInlineBoxPosition(position.deepEquivalent(), position.affinity());
-}
-
 EphemeralRange makeRange(const VisiblePosition&, const VisiblePosition&);
 
 CORE_EXPORT Position canonicalPositionOf(const Position&);