Use std::unique_ptr<> for WebTaskRunner::clone

components/scheduler/child/web_task_runner_impl.h

 // Copyright 2015 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 COMPONENTS_SCHEDULER_CHILD_WEB_TASK_RUNNER_H_
 #define COMPONENTS_SCHEDULER_CHILD_WEB_TASK_RUNNER_H_
 
 #include <memory>
 
 #include "base/macros.h"
@@ skipping 13 matching lines @@
 
   // blink::WebTaskRunner implementation:
   void postTask(const blink::WebTraceLocation& web_location,
                 blink::WebTaskRunner::Task* task) override;
   void postDelayedTask(const blink::WebTraceLocation& web_location,
                        blink::WebTaskRunner::Task* task,
                        double delayMs) override;
   bool runsTasksOnCurrentThread() override;
   double virtualTimeSeconds() const override;
   double monotonicallyIncreasingVirtualTimeSeconds() const override;
-  blink::WebTaskRunner* clone() override;
+  std::unique_ptr<blink::WebTaskRunner> clone() override;
 
   // blink::WebTaskRunner::Task should be wrapped by base::Passed() when
   // used with base::Bind(). See https://crbug.com/551356.
   // runTask() is a helper to call blink::WebTaskRunner::Task::run from
   // std::unique_ptr<blink::WebTaskRunner::Task>.
   // runTask() is placed here because std::unique_ptr<> cannot be used from
   // Blink.
   static void runTask(std::unique_ptr<blink::WebTaskRunner::Task>);
 
  private:
   base::TimeTicks Now() const;
 
   scoped_refptr<TaskQueue> task_queue_;
 
   DISALLOW_COPY_AND_ASSIGN(WebTaskRunnerImpl);
 };
 
 }  // namespace scheduler
 
 #endif  // COMPONENTS_SCHEDULER_CHILD_WEB_TASK_RUNNER_H_