Introduce OnceClosure and BindOnce

base/bind_internal.h

Index: base/bind_internal.h
diff --git a/base/bind_internal.h b/base/bind_internal.h
index 3d6ca09c41e4e31404a11bb16ad99a425bc6369c..7ad7493eacc4a5eba6c1b627ddaafdf0865a664a 100644
--- a/base/bind_internal.h
+++ b/base/bind_internal.h
@@ -244,14 +244,16 @@ struct FunctorTraits<IgnoreResultHelper<T>> : FunctorTraits<T> {
   template <typename IgnoreResultType, typename... RunArgs>
   static void Invoke(IgnoreResultType&& ignore_result_helper,
                      RunArgs&&... args) {
-    FunctorTraits<T>::Invoke(ignore_result_helper.functor_,
-                             std::forward<RunArgs>(args)...);
+    FunctorTraits<T>::Invoke(
+        std::forward<IgnoreResultType>(ignore_result_helper).functor_,
+        std::forward<RunArgs>(args)...);
   }
 };
 
 // For Callbacks.
-template <typename R, typename... Args, CopyMode copy_mode>
-struct FunctorTraits<Callback<R(Args...), copy_mode>> {
+template <typename R, typename... Args,
+          CopyMode copy_mode, RepeatMode repeat_mode>
+struct FunctorTraits<Callback<R(Args...), copy_mode, repeat_mode>> {
   using RunType = R(Args...);
   static constexpr bool is_method = false;
   static constexpr bool is_nullable = true;
@@ -327,6 +329,19 @@ struct Invoker<StorageType, R(UnboundArgs...)> {
                    std::forward<UnboundArgs>(unbound_args)...);
   }
 
+  static R RunOneShot(BindStateBase* base, UnboundArgs&&... unbound_args) {
+    // Local references to make debugger stepping easier. If in a debugger,
+    // you really want to warp ahead and step through the
+    // InvokeHelper<>::MakeItSo() call below.
+    StorageType* storage = static_cast<StorageType*>(base);
+    static constexpr size_t num_bound_args =
+        std::tuple_size<decltype(storage->bound_args_)>::value;
+    return RunImpl(std::move(storage->functor_),
+                   std::move(storage->bound_args_),
+                   MakeIndexSequence<num_bound_args>(),
+                   std::forward<UnboundArgs>(unbound_args)...);
+  }
+
  private:
   template <typename Functor, typename BoundArgsTuple, size_t... indices>
   static inline R RunImpl(Functor&& functor,
@@ -380,7 +395,7 @@ struct BindState final : BindStateBase {
   template <typename ForwardFunctor, typename... ForwardBoundArgs>
   explicit BindState(ForwardFunctor&& functor, ForwardBoundArgs&&... bound_args)
       : BindStateBase(&Destroy),
-      functor_(std::forward<ForwardFunctor>(functor)),
+        functor_(std::forward<ForwardFunctor>(functor)),
         bound_args_(std::forward<ForwardBoundArgs>(bound_args)...) {
     DCHECK(!IsNull(functor_));
   }