Make VisiblePosition::init to not use being constructed object

Source/core/editing/PositionWithAffinity.cpp

Index: Source/core/editing/PositionWithAffinity.cpp
diff --git a/Source/core/editing/PositionWithAffinity.cpp b/Source/core/editing/PositionWithAffinity.cpp
index fff00e05be23125f5d6518f5a56f0b0edbd40c68..50de54114602b0be1388aa140b685adae0b23ee1 100644
--- a/Source/core/editing/PositionWithAffinity.cpp
+++ b/Source/core/editing/PositionWithAffinity.cpp
@@ -25,6 +25,14 @@ PositionWithAffinityTemplate<PositionType>::~PositionWithAffinityTemplate()
 {
 }
 
+template <typename PositionType>
+bool PositionWithAffinityTemplate<PositionType>::operator==(const PositionWithAffinityTemplate& other) const
+{
+    if (isNull())
+        return other.isNull();
+    return m_affinity == other.m_affinity && m_position == other.m_position;
+}
+
 template class CORE_EXTERN_TEMPLATE_EXPORT PositionWithAffinityTemplate<Position>;
 
 } // namespace blink