Callback: De-inline CallbackBase, and move to callback_helpers -> callback_internal.h

base/callback_helpers.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.
-
-// This file contains utility functions and classes that help the
-// implementation, and management of the Callback objects.
-
-#ifndef BASE_CALLBACK_HELPERS_H_
-#define BASE_CALLBACK_HELPERS_H_
-#pragma once
-
-#include "base/ref_counted.h"
-
-namespace base {
-namespace internal {
-
-// InvokerStorageBase is used to provide an opaque handle that the Callback
-// class can use to represent a function object with bound arguments.  It
-// behaves as an existential type that is used by a corresponding
-// DoInvoke function to perform the function execution.  This allows
-// us to shield the Callback class from the types of the bound argument via
-// "type erasure."
-class InvokerStorageBase : public RefCountedThreadSafe<InvokerStorageBase> {
- protected:
-  friend class RefCountedThreadSafe<InvokerStorageBase>;
-  virtual ~InvokerStorageBase() {}
-};
-
-// This structure exists purely to pass the returned |invoker_storage_| from
-// Bind() to Callback while avoiding an extra AddRef/Release() pair.
-//
-// To do this, the constructor of Callback<> must take a const-ref.  The
-// reference must be to a const object otherwise the compiler will emit a
-// warning about taking a reference to a temporary.
-//
-// Unfortunately, this means that the internal |invoker_storage_| field must
-// be made mutable.
-template <typename T>
-struct InvokerStorageHolder {
-  explicit InvokerStorageHolder(T* invoker_storage)
-      : invoker_storage_(invoker_storage) {
-  }
-
-  mutable scoped_refptr<InvokerStorageBase> invoker_storage_;
-};
-
-template <typename T>
-InvokerStorageHolder<T> MakeInvokerStorageHolder(T* o) {
-  return InvokerStorageHolder<T>(o);
-}
-
-}  // namespace internal
-}  // namespace base
-
-#endif  // BASE_CALLBACK_HELPERS_H_