Introduce Position::IsEquivalent()

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

Index: third_party/WebKit/Source/core/editing/Position.cpp
diff --git a/third_party/WebKit/Source/core/editing/Position.cpp b/third_party/WebKit/Source/core/editing/Position.cpp
index 771328e27d55caed0c567d7e0dd7aec8c337b84d..eab61e4ba6df3f245d5175760b3664b13d1dca26 100644
--- a/third_party/WebKit/Source/core/editing/Position.cpp
+++ b/third_party/WebKit/Source/core/editing/Position.cpp
@@ -353,6 +353,16 @@ bool PositionTemplate<Strategy>::operator>=(
 }
 
 template <typename Strategy>
+bool PositionTemplate<Strategy>::IsEquivalent(
+    const PositionTemplate<Strategy>& other) const {
+  if (IsNull())
+    return other.IsNull();
+  if (anchor_type_ == other.anchor_type_)
+    return *this == other;
+  return ToOffsetInAnchor() == other.ToOffsetInAnchor();
+}
+
+template <typename Strategy>
 bool PositionTemplate<Strategy>::AtFirstEditingPositionForNode() const {
   if (IsNull())
     return true;