Introduce VisiblePosition::isValid

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

Index: third_party/WebKit/Source/core/editing/VisiblePosition.h
diff --git a/third_party/WebKit/Source/core/editing/VisiblePosition.h b/third_party/WebKit/Source/core/editing/VisiblePosition.h
index ffaab651d8adc7f529bcac23e32549e44ace65bf..5e17fb4f2599a9d12548b8327fbf9919b92f1cc0 100644
--- a/third_party/WebKit/Source/core/editing/VisiblePosition.h
+++ b/third_party/WebKit/Source/core/editing/VisiblePosition.h
@@ -85,6 +85,7 @@ public:
     bool isNull() const { return m_positionWithAffinity.isNull(); }
     bool isNotNull() const { return m_positionWithAffinity.isNotNull(); }
     bool isOrphan() const { return deepEquivalent().isOrphan(); }
+    bool isValid() const;
 
     PositionTemplate<Strategy> deepEquivalent() const { return m_positionWithAffinity.position(); }

[yosin_UTC9, 2016/09/20 13:55:51]

Should we have |DCHECK(isValid())| in |deepEquivalent()|? Is it too early to do
so?
If so, let's add |TODO| for |deepEquivalent()|.

[Xiaocheng, 2016/09/21 06:31:49]

I think we can't do that, at least for now.

Some clients store a VP and call deepEquivalent() after mutation. An example is
DragCaretController::setCaretPosition.

     PositionTemplate<Strategy> toParentAnchoredPosition() const { return deepEquivalent().parentAnchoredEquivalent(); }
@@ -111,6 +112,10 @@ private:
     explicit VisiblePositionTemplate(const PositionWithAffinityTemplate<Strategy>&);
 
     PositionWithAffinityTemplate<Strategy> m_positionWithAffinity;
+
+#if DCHECK_IS_ON()
+    uint64_t m_domTreeVersion;
+#endif
 };
 
 extern template class CORE_EXTERN_TEMPLATE_EXPORT VisiblePositionTemplate<EditingStrategy>;