Introduce VisiblePosition::isValid

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

Index: third_party/WebKit/Source/core/editing/VisiblePosition.cpp
diff --git a/third_party/WebKit/Source/core/editing/VisiblePosition.cpp b/third_party/WebKit/Source/core/editing/VisiblePosition.cpp
index a9187c09d098b1deaa903fcad6f959e989ae41a8..2d6b92804d351ff5583c4e40820bbb45b4076878 100644
--- a/third_party/WebKit/Source/core/editing/VisiblePosition.cpp
+++ b/third_party/WebKit/Source/core/editing/VisiblePosition.cpp
@@ -45,12 +45,20 @@ using namespace HTMLNames;
 
 template <typename Strategy>
 VisiblePositionTemplate<Strategy>::VisiblePositionTemplate()
+#if DCHECK_IS_ON()
+    : m_domTreeVersion(0)
+    , m_styleVersion(0)
+#endif
 {
 }
 
 template <typename Strategy>
 VisiblePositionTemplate<Strategy>::VisiblePositionTemplate(const PositionWithAffinityTemplate<Strategy>& positionWithAffinity)
     : m_positionWithAffinity(positionWithAffinity)
+#if DCHECK_IS_ON()
+    , m_domTreeVersion(positionWithAffinity.position().document()->domTreeVersion())
+    , m_styleVersion(positionWithAffinity.position().document()->styleVersion())
+#endif
 {
 }
 
@@ -214,6 +222,19 @@ void VisiblePositionTemplate<Strategy>::showTreeForThis() const
 
 #endif
 
+template <typename Strategy>
+bool VisiblePositionTemplate<Strategy>::isValid() const
+{
+#if DCHECK_IS_ON()
+    if (isNull())
+        return true;
+    Document& document = *m_positionWithAffinity.position().document();
+    return m_domTreeVersion == document.domTreeVersion() && m_styleVersion == document.styleVersion() && !document.needsLayoutTreeUpdate();
+#else
+    return true;
+#endif
+}
+
 template class CORE_TEMPLATE_EXPORT VisiblePositionTemplate<EditingStrategy>;
 template class CORE_TEMPLATE_EXPORT VisiblePositionTemplate<EditingInFlatTreeStrategy>;