Improve documentation and tests for base::OnTaskRunnerDeleter.

base/sequenced_task_runner.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_SEQUENCED_TASK_RUNNER_H_
 #define BASE_SEQUENCED_TASK_RUNNER_H_
 
 #include <memory>
 
 #include "base/base_export.h"
@@ skipping 136 matching lines @@
 
  protected:
   ~SequencedTaskRunner() override {}
 
  private:
   bool DeleteOrReleaseSoonInternal(const tracked_objects::Location& from_here,
                                    void (*deleter)(const void*),
                                    const void* object);
 };
 
+// Sample usage with std::unique_ptr :
+// std::unique_ptr<Foo, base::OnTaskRunnerDeleter> ptr(
+//     new Foo, base::OnTaskRunnerDeleter(my_task_runner));
+//
+// TODO: RefCounted isn't yet supported per RefCountedTraits using a static
+// deleter and thus not be bindable to a specific TaskRunner.
 struct BASE_EXPORT OnTaskRunnerDeleter {
   explicit OnTaskRunnerDeleter(scoped_refptr<SequencedTaskRunner> task_runner);
   ~OnTaskRunnerDeleter();
 
   OnTaskRunnerDeleter(OnTaskRunnerDeleter&&);
   OnTaskRunnerDeleter& operator=(OnTaskRunnerDeleter&&);
 
+  // For compatibility with std:: deleters.
   template <typename T>
   void operator()(const T* ptr) {
     if (ptr)
       task_runner_->DeleteSoon(FROM_HERE, ptr);
   }
 
   scoped_refptr<SequencedTaskRunner> task_runner_;
 };
 
 }  // namespace base
 
 #endif  // BASE_SEQUENCED_TASK_RUNNER_H_