Remove "delete this" pattern from UsbContext completely.

device/usb/usb_context.h

 // Copyright 2014 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 DEVICE_USB_USB_CONTEXT_H_
 #define DEVICE_USB_USB_CONTEXT_H_
 
 #include "base/basictypes.h"
 #include "base/memory/ref_counted.h"
 #include "base/memory/scoped_ptr.h"
@@ skipping 15 matching lines @@
 
  protected:
   friend class UsbServiceImpl;
   friend class base::RefCountedThreadSafe<UsbContext>;
 
   explicit UsbContext(PlatformUsbContext context);
   virtual ~UsbContext();
 
  private:
   class UsbEventHandler;
+
   PlatformUsbContext context_;
-  UsbEventHandler* event_handler_;
+  scoped_ptr<UsbEventHandler> event_handler_;
   base::ThreadChecker thread_checker_;
 
   DISALLOW_COPY_AND_ASSIGN(UsbContext);
 };
 
 }  // namespace device
 
 #endif  // DEVICE_USB_USB_CONTEXT_H_