[CodeHealth][Editing] Refactor EphemeralRange::isNull/isNotNull impl.

Source/core/editing/EphemeralRange.h

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef EphemeralRange_h
 #define EphemeralRange_h
 
 #include "core/editing/Position.h"
 
 namespace blink {
@@ skipping 22 matching lines @@
 //  Because of |Range| objects consume heap memory and inserted into |Range|
 //  object list in |Document| for relocation. These operations are redundant
 //  if |Range| objects doesn't live after DOM mutation.
 //
 template <typename Strategy>
 class CORE_TEMPLATE_CLASS_EXPORT EphemeralRangeTemplate final {
     STACK_ALLOCATED();
 public:
     EphemeralRangeTemplate(const PositionAlgorithm<Strategy>& start, const PositionAlgorithm<Strategy>& end);
     EphemeralRangeTemplate(const EphemeralRangeTemplate& other);
-    // |position| should be null or in-document.
+    // |position| should be |Position::isNull()| or in-document.
     explicit EphemeralRangeTemplate(const PositionAlgorithm<Strategy>& /* position */);
-    // When |range| is nullptr, |EphemeralRangeTemplate| is null.
+    // When |range| is nullptr, |EphemeralRangeTemplate| is |isNull()|.
     explicit EphemeralRangeTemplate(const Range* /* range */);
     EphemeralRangeTemplate();
     ~EphemeralRangeTemplate();
 
     EphemeralRangeTemplate<Strategy>& operator=(const EphemeralRangeTemplate<Strategy>& other);
 
     bool operator==(const EphemeralRangeTemplate<Strategy>& other) const;
     bool operator!=(const EphemeralRangeTemplate<Strategy>& other) const;
 
     Document& document() const;
     PositionAlgorithm<Strategy> startPosition() const;
     PositionAlgorithm<Strategy> endPosition() const;
 
     // Returns true if |m_startPositoin| == |m_endPosition| or |isNull()|.
     bool isCollapsed() const;
-    bool isNull() const { return !isNotNull(); }
-    bool isNotNull() const;
+    bool isNull() const
+    {
+        ASSERT(isValid());
+        return m_startPosition.isNull();
+    }
+    bool isNotNull() const { return !isNull(); }
 
     DEFINE_INLINE_TRACE()
     {
         visitor->trace(m_startPosition);
         visitor->trace(m_endPosition);
     }
 
     // |node| should be in-document and valid for anchor node of
     // |PositionAlgorithm<Strategy>|.
     static EphemeralRangeTemplate<Strategy> rangeOfContents(const Node& /* node */);
@@ skipping 14 matching lines @@
 extern template class CORE_EXTERN_TEMPLATE_EXPORT EphemeralRangeTemplate<EditingInComposedTreeStrategy>;
 using EphemeralRangeInComposedTree = EphemeralRangeTemplate<EditingInComposedTreeStrategy>;
 
 // Returns a newly created |Range| object from |range| or |nullptr| if
 // |range.isNull()| returns true.
 CORE_EXPORT PassRefPtrWillBeRawPtr<Range> createRange(const EphemeralRange& /* range */);
 
 } // namespace blink
 
 #endif