Pass weak pointer by ref in Bind implementation

base/bind_internal.h

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef BASE_BIND_INTERNAL_H_
 #define BASE_BIND_INTERNAL_H_
 
 #include <stddef.h>
 
 #include <tuple>
@@ skipping 277 matching lines @@
 template <typename ReturnType>
 struct InvokeHelper<true, ReturnType> {
   // WeakCalls are only supported for functions with a void return type.
   // Otherwise, the function result would be undefined if the the WeakPtr<>
   // is invalidated.
   static_assert(std::is_void<ReturnType>::value,
                 "weak_ptrs can only bind to methods without return values");
 
   template <typename Functor, typename BoundWeakPtr, typename... RunArgs>
   static inline void MakeItSo(Functor&& functor,
-                              BoundWeakPtr weak_ptr,
+                              BoundWeakPtr&& weak_ptr,
                               RunArgs&&... args) {
     if (!weak_ptr)
       return;
     using Traits = FunctorTraits<typename std::decay<Functor>::type>;
     Traits::Invoke(std::forward<Functor>(functor),
                    std::forward<BoundWeakPtr>(weak_ptr),
                    std::forward<RunArgs>(args)...);
   }
 };
 
@@ skipping 135 matching lines @@
 
 // Returns a RunType of bound functor.
 // E.g. MakeUnboundRunType<R(A, B, C), A, B> is evaluated to R(C).
 template <typename Functor, typename... BoundArgs>
 using MakeUnboundRunType =
     typename internal::MakeUnboundRunTypeImpl<Functor, BoundArgs...>::Type;
 
 }  // namespace base
 
 #endif  // BASE_BIND_INTERNAL_H_