Turn Scope::locals_ into a ThreadedList

src/utils.h

Index: src/utils.h
diff --git a/src/utils.h b/src/utils.h
index dcc4756a36de0ef258c415a2d9321b0853795393..75937fa2ab464c8896c3bf21f1a2bf8a51aa30e9 100644
--- a/src/utils.h
+++ b/src/utils.h
@@ -1648,6 +1648,15 @@ class ThreadedList final {
     *tail_ = nullptr;
   }
 
+  void MoveTail(ThreadedList<T>& parent, Iterator location) {

[adamk, 2016/11/02 18:54:05]

Please make this a pointer, I don't think we generally use non-const references
like this.

Also this method could use a comment.

+    if (parent.end() != location) {
+      DCHECK_NULL(*tail_);
+      *tail_ = *location;
+      tail_ = parent.tail_;
+      parent.Rewind(location);
+    }
+  }
+
   bool is_empty() const { return head_ == nullptr; }
 
   // Slow. For testing purposes.