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

Replace null with isNull in comment because 'null' means nullptr typically.
We prefer not to use double negation so reverse impl in isNull and isNotNull.
It gets straightforward.

BUG=

Review URL: https://codereview.chromium.org/1318913004

git-svn-id: svn://svn.chromium.org/blink/trunk@201297 bbb929c8-8fbe-4397-9dbb-9b2b20218538

third_party/WebKit/Source/core/editing/EphemeralRange.cpp

@@ -117,13 +117,6 @@ bool EphemeralRangeTemplate<Strategy>::isCollapsed() const
     return m_startPosition == m_endPosition;
 }
 
-template <typename Strategy>
-bool EphemeralRangeTemplate<Strategy>::isNotNull() const
-{
-    ASSERT(isValid());
-    return m_startPosition.isNotNull();
-}
-
 template <typename Strategy>
 EphemeralRangeTemplate<Strategy> EphemeralRangeTemplate<Strategy>::rangeOfContents(const Node& node)
 {

third_party/WebKit/Source/core/editing/EphemeralRange.h

@@ -40,9 +40,9 @@ class CORE_TEMPLATE_CLASS_EXPORT EphemeralRangeTemplate final {
 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();
@@ -58,8 +58,12 @@ public:
 
     // 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()
     {