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..ce4c3e7192d4d58571ccadf67c7661898c5357a2 100644
--- a/base/callback_forward.h
+++ b/base/callback_forward.h
@@ -12,19 +12,40 @@ namespace internal {
 // MoveOnly indicates the Callback is not copyable but movable, and Copyable
 // indicates it is copyable and movable.
 enum class CopyMode {
-  MoveOnly, Copyable,
+  MoveOnly,
+  Copyable,
+};
+
+enum class RepeatMode {
+  Once,
+  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;
 
 // 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()>;
 
+namespace internal {
+
+template <typename Signature>
+using OnceCallback = Callback<Signature,
+                              internal::CopyMode::MoveOnly,
+                              internal::RepeatMode::Once>;
+template <typename Signature>
+using RepeatingCallback = Callback<Signature,
+                                   internal::CopyMode::Copyable,
+                                   internal::RepeatMode::Repeating>;
+using OnceClosure = OnceCallback<void()>;
+using RepeatingClosure = RepeatingCallback<void()>;
+
+}  // namespace internal
 }  // namespace base
 
 #endif  // BASE_CALLBACK_FORWARD_H_