Stop accepting a null reply in base::PostTaskAndReplyWithResult().

base/task_runner_util.h

 // 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.
 
 #ifndef BASE_TASK_RUNNER_UTIL_H_
 #define BASE_TASK_RUNNER_UTIL_H_
 
 #include "base/bind.h"
 #include "base/bind_helpers.h"
 #include "base/logging.h"
 #include "base/task_runner.h"
 
 namespace base {
 
 namespace internal {
 
 // Adapts a function that produces a result via a return value to
 // one that returns via an output parameter.
 template <typename ReturnType>
 void ReturnAsParamAdapter(const Callback<ReturnType(void)>& func,
                           ReturnType* result) {
   *result = func.Run();
 }
 
 // Adapts a T* result to a callblack that expects a T.
 template <typename TaskReturnType, typename ReplyArgType>
 void ReplyAdapter(const Callback<void(ReplyArgType)>& callback,
                   TaskReturnType* result) {
-  // TODO(ajwong): Remove this conditional and add a DCHECK to enforce that
-  // |reply| must be non-null in PostTaskAndReplyWithResult() below after
-  // current code that relies on this API softness has been removed.
-  // http://crbug.com/162712
-  if (!callback.is_null())
-    callback.Run(std::move(*result));
+  callback.Run(std::move(*result));
 }
 
 }  // namespace internal
 
 // When you have these methods
 //
 //   R DoWorkAndReturn();
 //   void Callback(const R& result);
 //
 // and want to call them in a PostTaskAndReply kind of fashion where the
 // result of DoWorkAndReturn is passed to the Callback, you can use
 // PostTaskAndReplyWithResult as in this example:
 //
 // PostTaskAndReplyWithResult(
 //     target_thread_.task_runner(),
 //     FROM_HERE,
 //     Bind(&DoWorkAndReturn),
 //     Bind(&Callback));
 template <typename TaskReturnType, typename ReplyArgType>
 bool PostTaskAndReplyWithResult(
     TaskRunner* task_runner,
     const tracked_objects::Location& from_here,
     const Callback<TaskReturnType(void)>& task,
     const Callback<void(ReplyArgType)>& reply) {
+  DCHECK(task);
+  DCHECK(reply);

[dcheng, 2016/11/29 21:13:11]

TIL that Callback can convert to bool.

   TaskReturnType* result = new TaskReturnType();
   return task_runner->PostTaskAndReply(
       from_here,
       base::Bind(&internal::ReturnAsParamAdapter<TaskReturnType>, task,
                  result),
       base::Bind(&internal::ReplyAdapter<TaskReturnType, ReplyArgType>, reply,
                  base::Owned(result)));
 }
 
 }  // namespace base
 
 #endif  // BASE_TASK_RUNNER_UTIL_H_