Drop unnecessary NodeWithIndex::m_haveIndex data member

Source/core/dom/NodeWithIndex.h

Index: Source/core/dom/NodeWithIndex.h
diff --git a/Source/core/dom/NodeWithIndex.h b/Source/core/dom/NodeWithIndex.h
index 02b6d33c15acdadcd3abdffe27003c6f37e2500e..a67c7bb714fa8e393084136269c385e3a916e56f 100644
--- a/Source/core/dom/NodeWithIndex.h
+++ b/Source/core/dom/NodeWithIndex.h
@@ -36,7 +36,7 @@ class NodeWithIndex {
 public:
     explicit NodeWithIndex(Node& node)
         : m_node(node)
-        , m_haveIndex(false)
+        , m_index(-1)

[eseidel, 2014/06/02 05:14:10]

Why was m_index not initialized before?  I guess it didn't need to be...

[Inactive, 2014/06/02 12:10:22]

Yes, it wasn't because it did not need to be (access to m_index was always
protected by checking m_haveIndex). However, I don't believe we are trading
speed since the previous code has to initialize m_haveIndex anyway.

     {
     }
 
@@ -44,17 +44,16 @@ public:
 
     int index() const
     {
-        if (!m_haveIndex) {
+        if (!hasIndex())
             m_index = m_node.nodeIndex();

[eseidel, 2014/06/02 05:14:42]

Can this ever return negative?

[Jeffrey Yasskin, 2014/06/02 06:06:16]

It would be good to ASSERT that hasIndex() after this line.

[Inactive, 2014/06/02 12:10:22]

No it cannot, this is why my change is safe. As explained in the Changelog,
nodeIndex() returns an unsigned integer:
unsigned nodeIndex() const;

[Inactive, 2014/06/02 12:10:22]

Makes sense, will do.

[Inactive, 2014/06/02 12:12:20]

Done.

-            m_haveIndex = true;
-        }
         ASSERT(m_index == static_cast<int>(m_node.nodeIndex()));
         return m_index;
     }
 
 private:
+    bool hasIndex() const { return m_index >= 0; }
+
     Node& m_node;
-    mutable bool m_haveIndex;
     mutable int m_index;
 };