Introduce OnceClosure and BindOnce

base/callback_internal.cc

 // Copyright (c) 2012 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.
 
 #include "base/callback_internal.h"
 
 #include "base/logging.h"
 
 namespace base {
 namespace internal {
 
 void BindStateBase::AddRef() {
   AtomicRefCountInc(&ref_count_);
 }
 
 void BindStateBase::Release() {
   if (!AtomicRefCountDec(&ref_count_))
     destructor_(this);
 }
 
 CallbackBase<CopyMode::MoveOnly>::CallbackBase(CallbackBase&& c) = default;
 
 CallbackBase<CopyMode::MoveOnly>&
 CallbackBase<CopyMode::MoveOnly>::operator=(CallbackBase&& c) = default;
 
+CallbackBase<CopyMode::MoveOnly>::CallbackBase(
+    const CallbackBase<CopyMode::Copyable>& c)
+    : bind_state_(c.bind_state_), polymorphic_invoke_(c.polymorphic_invoke_) {}
+
+CallbackBase<CopyMode::MoveOnly>& CallbackBase<CopyMode::MoveOnly>::operator=(
+    const CallbackBase<CopyMode::Copyable>& c) {
+  bind_state_ = c.bind_state_;
+  polymorphic_invoke_ = c.polymorphic_invoke_;
+  return *this;
+}
+
 void CallbackBase<CopyMode::MoveOnly>::Reset() {
   polymorphic_invoke_ = nullptr;
   // NULL the bind_state_ last, since it may be holding the last ref to whatever
   // object owns us, and we may be deleted after that.
   bind_state_ = nullptr;
 }
 
 bool CallbackBase<CopyMode::MoveOnly>::EqualsInternal(
     const CallbackBase& other) const {
   // Ignore |polymorphic_invoke_| value in null case.
@@ skipping 28 matching lines @@
 }
 
 CallbackBase<CopyMode::Copyable>&
 CallbackBase<CopyMode::Copyable>::operator=(CallbackBase&& c) = default;
 
 template class CallbackBase<CopyMode::MoveOnly>;
 template class CallbackBase<CopyMode::Copyable>;
 
 }  // namespace internal
 }  // namespace base