Introduce Position constructor with const Node&

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

 /*
  * Copyright (C) 2004, 2005, 2006, 2009 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
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  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 95 matching lines @@
     DCHECK(IsBeforeChildren() || IsAfterChildren()) << anchor_type_;
     return;
   }
 #if DCHECK_IS_ON()
   DCHECK(CanBeAnchorNode<Strategy>(anchor_node_.Get())) << anchor_node_;
 #endif
   DCHECK_NE(anchor_type_, PositionAnchorType::kOffsetInAnchor);
 }
 
 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_)
     DCHECK_GE(offset, 0);
   else
     DCHECK_EQ(offset, 0);
 #if DCHECK_IS_ON()
   DCHECK(CanBeAnchorNode<Strategy>(anchor_node_.Get())) << anchor_node_;
 #endif
 }
 
 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_),
       anchor_type_(other.anchor_type_) {}
 
 // --
 
 template <typename Strategy>
 Node* PositionTemplate<Strategy>::ComputeContainerNode() const {
   if (!anchor_node_)
@@ skipping 564 matching lines @@
 }
 
 void showTree(const blink::Position* pos) {
   if (pos)
     pos->ShowTreeForThis();
   else
     LOG(INFO) << "Cannot showTree for <null>";
 }
 
 #endif