Adding use_system_libusb option for third_party/libusb

chrome/browser/usb/usb_service.cc

 // 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.
 
 #include "chrome/browser/usb/usb_service.h"
 
 #include "base/bind.h"
 #include "base/bind_helpers.h"
 #include "base/stl_util.h"
 #include "chrome/browser/usb/usb_device.h"
-#include "third_party/libusb/libusb/libusb.h"
+#include "third_party/libusb/libusb.h"
 
 UsbService::UsbService() : running_(true), thread_("UsbThread") {
   libusb_init(&context_);
   thread_.Start();
   PostHandleEventTask();
 }
 
 UsbService::~UsbService() {}
 
 // TODO(gdk): There is currently no clean way to indicate to the event handler
@@ skipping 46 matching lines @@
     }
   }
 }
 
 void UsbService::PostHandleEventTask() {
   thread_.message_loop()->PostTask(FROM_HERE, base::Bind(
       &UsbService::HandleEvent, base::Unretained(this)));
 }
 
 void UsbService::HandleEvent() {
-  libusb_handle_events_completed(context_, NULL);
+  // TODO(gdk): Once there is a reasonable expectation that platforms will use

[Paweł Hajdan Jr., 2012/05/10 06:36:15]

Note: there is. Gentoo Linux doesn't even have any older libusb.

Depending on whether libusb_handle_events is broken with 1.0.9, or
libusb_handle_events_completed is not present in older versions, the more
compatible one should be kept (don't worry about the system lib on Ubuntu; if
your bundled libusb is 1.0.9, feel free to use 1.0.9 call).

[Garret Kelly, 2012/05/10 17:44:01]

I'll leave the older call for compatibility's sake, it's not going to be removed
from the libusb API at any point.

+  // libusb >= 1.0.9 this should be changed to handle_events_completed, as the
+  // use of handle_events is deprecated.
+  libusb_handle_events(context_);
   if (running_) {
     PostHandleEventTask();
   }
 }
 
 void UsbService::PlatformShutdown() {
   libusb_exit(context_);
 }