Revert 114494 - Remove BindStateHolder and have Bind() return a Callback<> object directly.

base/callback_internal.h

Index: base/callback_internal.h
===================================================================
--- base/callback_internal.h	(revision 114494)
+++ base/callback_internal.h	(working copy)
@@ -29,6 +29,29 @@
   virtual ~BindStateBase() {}
 };
 
+// This structure exists purely to pass the returned |bind_state_| from
+// Bind() to Callback while avoiding an extra AddRef/Release() pair.
+//
+// To do this, the constructor of Callback<> must take a const-ref.  The
+// reference must be to a const object otherwise the compiler will emit a
+// warning about taking a reference to a temporary.
+//
+// Unfortunately, this means that the internal |bind_state_| field must
+// be made mutable.
+template <typename T>
+struct BindStateHolder {
+  explicit BindStateHolder(T* bind_state)
+      : bind_state_(bind_state) {
+  }
+
+  mutable scoped_refptr<BindStateBase> bind_state_;
+};
+
+template <typename T>
+BindStateHolder<T> MakeBindStateHolder(T* o) {
+  return BindStateHolder<T>(o);
+}
+
 // Holds the Callback methods that don't require specialization to reduce
 // template bloat.
 class BASE_EXPORT CallbackBase {
@@ -49,11 +72,8 @@
   // Returns true if this callback equals |other|. |other| may be null.
   bool Equals(const CallbackBase& other) const;
 
-  // Allow initializing of |bind_state_| via the constructor to avoid default
-  // initialization of the scoped_refptr.  We do not also initialize
-  // |polymorphic_invoke_| here because doing a normal assignment in the
-  // derived Callback templates makes for much nicer compiler errors.
-  explicit CallbackBase(BindStateBase* bind_state);
+  CallbackBase(InvokeFuncStorage polymorphic_invoke,
+               scoped_refptr<BindStateBase>* bind_state);
 
   // Force the destructor to be instantiated inside this translation unit so
   // that our subclasses will not get inlined versions.  Avoids more template