Make navigator.usb open the DeviceManager connection lazily.

third_party/WebKit/Source/modules/webusb/USB.h

 // 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.
 
 #ifndef USB_h
 #define USB_h
 
 #include "bindings/core/v8/ScriptPromise.h"
 #include "bindings/core/v8/ScriptWrappable.h"
 #include "core/dom/ContextLifecycleObserver.h"
@@ skipping 51 matching lines @@
 
   // DeviceManagerClient implementation.
   void OnDeviceAdded(device::usb::blink::DeviceInfoPtr);
   void OnDeviceRemoved(device::usb::blink::DeviceInfoPtr);
 
   void onDeviceManagerConnectionError();
   void onChooserServiceConnectionError();
 
   DECLARE_VIRTUAL_TRACE();
 
+ protected:
+  // EventTarget protected overrides.
+  void addedEventListener(const AtomicString& eventType,
+                          RegisteredEventListener&) override;
+
  private:
   explicit USB(LocalFrame& frame);
 
+  void ensureDeviceManagerConnection();
+
   device::usb::blink::DeviceManagerPtr m_deviceManager;
   HeapHashSet<Member<ScriptPromiseResolver>> m_deviceManagerRequests;
   device::usb::blink::ChooserServicePtr m_chooserService;
   HeapHashSet<Member<ScriptPromiseResolver>> m_chooserServiceRequests;
   mojo::Binding<device::usb::blink::DeviceManagerClient> m_clientBinding;
   HeapHashMap<String, WeakMember<USBDevice>> m_deviceCache;
 };
 
 }  // namespace blink
 
 #endif  // USB_h