Introduce OnceClosure and BindOnce

base/callback_forward.h

Index: base/callback_forward.h
diff --git a/base/callback_forward.h b/base/callback_forward.h
index 8b9b89cdc231bcf1020111e91bcbda14fd4e678c..5e0af872bf9039072912cbeb49ff8f949ca83f61 100644
--- a/base/callback_forward.h
+++ b/base/callback_forward.h
@@ -15,15 +15,32 @@ enum class CopyMode {
   MoveOnly, Copyable,
 };
 
+enum class RepeatMode {
+  OneShot,
+  Repeating,
+};
+
 }  // namespace internal
 
 template <typename Signature,
-          internal::CopyMode copy_mode = internal::CopyMode::Copyable>
+          internal::CopyMode copy_mode = internal::CopyMode::Copyable,
+          internal::RepeatMode repeat_mode = internal::RepeatMode::Repeating>
 class Callback;
 
+template <typename Signature>
+using RepeatingCallback = Callback<Signature,
+                                   internal::CopyMode::Copyable,
+                                   internal::RepeatMode::Repeating>;
+template <typename Signature>
+using OneShotCallback = Callback<Signature,
+                                 internal::CopyMode::MoveOnly,
+                                 internal::RepeatMode::OneShot>;
+
 // Syntactic sugar to make Callback<void()> easier to declare since it
 // will be used in a lot of APIs with delayed execution.
 using Closure = Callback<void()>;
+using RepeatingClosure = RepeatingCallback<void()>;
+using OneShotClosure = OneShotCallback<void()>;
 
 }  // namespace base