Delay WebUSB initialization until after browser startup.

chrome/browser/usb/web_usb_detector.cc

 // 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.
 
 #include "chrome/browser/usb/web_usb_detector.h"
 
 #include <utility>
 
 #include "base/macros.h"
 #include "base/metrics/histogram_macros.h"
@@ skipping 95 matching lines @@
 
   GURL landing_page_;
   std::string notification_id_;
   bool clicked_ = false;
 
   DISALLOW_COPY_AND_ASSIGN(WebUsbNotificationDelegate);
 };
 
 }  // namespace
 
-WebUsbDetector::WebUsbDetector() : observer_(this) {
-  Initialize();
-}
+WebUsbDetector::WebUsbDetector() : observer_(this) {}
 
 WebUsbDetector::~WebUsbDetector() {}
 
 void WebUsbDetector::Initialize() {
+  SCOPED_UMA_HISTOGRAM_TIMER("WebUsb.DetectorInitialization");
   device::UsbService* usb_service =
       device::DeviceClient::Get()->GetUsbService();
   if (!usb_service)
     return;
 
   observer_.Add(usb_service);
 }
 
 void WebUsbDetector::OnDeviceAdded(scoped_refptr<device::UsbDevice> device) {
   const base::string16& product_name = device->product_string();
@@ skipping 31 matching lines @@
 }
 
 void WebUsbDetector::OnDeviceRemoved(scoped_refptr<device::UsbDevice> device) {
   std::string notification_id = device->guid();
   message_center::MessageCenter* message_center =
       message_center::MessageCenter::Get();
   if (message_center->FindVisibleNotificationById(notification_id)) {
     message_center->RemoveNotification(notification_id, false /* by_user */);
   }
 }