Introduce Position constructor with const Node&

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 eab61e4ba6df3f245d5175760b3664b13d1dca26..4e4e69fedc9fb1acf33d7f80b3e6fead711ea22e 100644
--- a/third_party/WebKit/Source/core/editing/Position.cpp
+++ b/third_party/WebKit/Source/core/editing/Position.cpp
@@ -113,8 +113,9 @@ PositionTemplate<Strategy>::PositionTemplate(Node* anchor_node,
 }
 
 template <typename Strategy>
-PositionTemplate<Strategy>::PositionTemplate(Node* anchor_node, int offset)
-    : anchor_node_(anchor_node),
+PositionTemplate<Strategy>::PositionTemplate(const Node* anchor_node,
+                                             int offset)
+    : anchor_node_(const_cast<Node*>(anchor_node)),

[Xiaocheng, 2017/06/20 17:58:10]

I'm not a fan of this... It makes code less intuitive that, after constructing a
Position with a |const Node*|, you can still modify the node with the Position.

In some sense, a Position is kind of like a pointer. So maybe we should have
Position and ConstPosition?

[yosin_UTC9, 2017/06/21 04:27:02]

Discuss offline.
We agree on |Position| is constant, we should not change tree structure around
|anchor_node_|.
Thus, |anchor_node_| should be |Member<const Node>| and member functions in
|Position| should
return |const Node*|.

I file the issue[1] for tracking. 
In this patch, I will add TODO for it.

[1] http://crbug.com/735327 ⚐	Position should hold const Node instead of Node

       offset_(offset),
       anchor_type_(PositionAnchorType::kOffsetInAnchor) {
   if (anchor_node_)
@@ -127,6 +128,11 @@ PositionTemplate<Strategy>::PositionTemplate(Node* anchor_node, int offset)
 }
 
 template <typename Strategy>
+PositionTemplate<Strategy>::PositionTemplate(const Node& anchor_node,
+                                             int offset)
+    : PositionTemplate(&anchor_node, offset) {}
+
+template <typename Strategy>
 PositionTemplate<Strategy>::PositionTemplate(const PositionTemplate& other)
     : anchor_node_(other.anchor_node_),
       offset_(other.offset_),