Introduce isVisuallyEquivalentCandidate() as replacement of PositionAlgorithm::isCandidate()

Source/core/editing/Position.h

Index: Source/core/editing/Position.h
diff --git a/Source/core/editing/Position.h b/Source/core/editing/Position.h
index e52eb086ebaa5d9314fb896aa48e4e0e7364fa8d..6aa73a495a5194e87d2d23ca466b116a28cf3a96 100644
--- a/Source/core/editing/Position.h
+++ b/Source/core/editing/Position.h
@@ -187,8 +187,6 @@ public:
     PositionAlgorithm<Strategy> upstream(EditingBoundaryCrossingRule = CannotCrossEditingBoundary) const;
     PositionAlgorithm<Strategy> downstream(EditingBoundaryCrossingRule = CannotCrossEditingBoundary) const;
 
-    bool isCandidate() const;
-
     static PositionAlgorithm<Strategy> beforeNode(Node* anchorNode);
     static PositionAlgorithm<Strategy> afterNode(Node* anchorNode);
     static PositionAlgorithm<Strategy> inParentBeforeNode(const Node& anchorNode);
@@ -444,6 +442,11 @@ CORE_EXPORT bool inRenderedText(const PositionInComposedTree&);
 CORE_EXPORT int uncheckedPreviousOffset(const Node*, int current);
 CORE_EXPORT int uncheckedNextOffset(const Node*, int current);
 
+// TODO(yosin) We should move |isVisuallyEquivalentCandidate()| to
+// "VisibleUnits.cpp" to reduce |LayoutObject| dependency in "Position.cpp".
+CORE_EXPORT bool isVisuallyEquivalentCandidate(const Position&);
+CORE_EXPORT bool isVisuallyEquivalentCandidate(const PositionInComposedTree&);
+
 } // namespace blink
 
 #ifndef NDEBUG