repro for crbug.com/663886

base/callback_forward.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.
 
 #ifndef BASE_CALLBACK_FORWARD_H_
 #define BASE_CALLBACK_FORWARD_H_
 
 namespace base {
 namespace internal {
 
@@ skipping 27 matching lines @@
                               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 base
 
+namespace base {
+namespace dupe {
+namespace internal {
+
+// CopyMode is used to control the copyablity of a Callback.
+// MoveOnly indicates the Callback is not copyable but movable, and Copyable
+// indicates it is copyable and movable.
+enum class CopyMode {
+  MoveOnly,
+  Copyable,
+};
+
+enum class RepeatMode {
+  Once,
+  Repeating,
+};
+
+}  // namespace internal
+
+template <typename Signature,
+          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()>;
+
+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 base
 #endif  // BASE_CALLBACK_FORWARD_H_