exo: Fix crash in out-of-order destruction of Gamepad

components/exo/gamepad.cc

 // Copyright 2016 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.
 
 #include "components/exo/gamepad.h"
 
 #include <cmath>
 
 #include "ash/shell.h"
 #include "base/bind.h"
@@ skipping 123 matching lines @@
     SchedulePollOnPollingThread();
   }
 
   // Callback to ProcessGamepadChanges using weak reference to Gamepad.
   ProcessGamepadChangesCallback process_gamepad_changes_;
 
   // Callback method to create a gamepad data fetcher.
   CreateGamepadDataFetcherCallback create_fetcher_callback_;
 
   // Reference to task runner on polling thread.
-  base::SingleThreadTaskRunner* polling_task_runner_;
+  scoped_refptr<base::SingleThreadTaskRunner> polling_task_runner_;
 
   // Reference to task runner on origin thread.
   scoped_refptr<base::SingleThreadTaskRunner> origin_task_runner_;
 
   // Gamepad data fetcher used for querying gamepad devices.
   std::unique_ptr<device::GamepadDataFetcher> fetcher_;
 
   // The current state of all gamepads.
   blink::WebGamepads state_;
 
@@ skipping 101 matching lines @@
       delegate_->OnButton(button_id, new_button.pressed, new_button.value);
     }
   }
   if (send_frame)
     delegate_->OnFrame();
 
   pad_state_ = new_pad;
 }
 
 }  // namespace exo