Fail gracefully when libusb_init fails

chrome/browser/usb/usb_context.cc

 // Copyright 2013 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_context.h"
 
 #include "base/logging.h"
 #include "base/synchronization/waitable_event.h"
 #include "base/threading/platform_thread.h"
 #include "content/public/browser/browser_thread.h"
@@ skipping 42 matching lines @@
   VLOG(1) << "UsbEventHandler started.";
   if (running_) {
     start_polling_.Signal();
     libusb_handle_events(context_);
   }
   while (running_)
     libusb_handle_events(context_);
   VLOG(1) << "UsbEventHandler shutting down.";
 }
 
-UsbContext::UsbContext() : context_(NULL) {
+UsbContext::UsbContext(PlatformUsbContext context) : context_(context) {
   DCHECK(thread_checker_.CalledOnValidThread());
-  CHECK_EQ(0, libusb_init(&context_)) << "Cannot initialize libusb";
   event_handler_ = new UsbEventHandler(context_);
 }
 
 UsbContext::~UsbContext() {
   // destruction of UsbEventHandler is a blocking operation.
   DCHECK(thread_checker_.CalledOnValidThread());
   delete event_handler_;
   event_handler_ = NULL;
   libusb_exit(context_);
 }