Start BindStateBase ref count from 1 instead of 0

base/memory/ref_counted.h

Index: base/memory/ref_counted.h
diff --git a/base/memory/ref_counted.h b/base/memory/ref_counted.h
index ff46e6d6e5a9c87782b449474fbbebc4e0865454..c8564368b7f42836a4de01ba0699ea1f718a5f8e 100644
--- a/base/memory/ref_counted.h
+++ b/base/memory/ref_counted.h
@@ -385,6 +385,12 @@ class scoped_refptr {
   T* ptr_ = nullptr;
 
  private:
+  template <typename U>
+  friend scoped_refptr<U> AdoptRef(U*);
+
+  struct AdoptRefTag {};

[dcheng, 2017/03/06 22:09:18]

FWIW, the usual trick I've seen in the past is to use an enum here: for example,
see
https://cs.chromium.org/chromium/src/third_party/WebKit/Source/platform/webor...

[tzik, 2017/03/07 13:39:42]

Done.

+  scoped_refptr(T* p, AdoptRefTag) : ptr_(p) {}
+
   // Friend required for move constructors that set r.ptr_ to null.
   template <typename U>
   friend class scoped_refptr;
@@ -416,6 +422,16 @@ scoped_refptr<T> make_scoped_refptr(T* t) {
   return scoped_refptr<T>(t);
 }
 
+// Creates a scoped_refptr from a raw pointer without incrementing the reference
+// count. Use this only for a newly created object whose reference count starts
+// from 1 instead of 0.
+template <typename T>
+scoped_refptr<T> AdoptRef(T* t) {
+  DCHECK(!t || t->HasOneRef());
+  using Tag = typename scoped_refptr<T>::AdoptRefTag;
+  return scoped_refptr<T>(t, Tag());
+}
+
 template <typename T, typename U>
 bool operator==(const scoped_refptr<T>& lhs, const U* rhs) {
   return lhs.get() == rhs;