Add device path enumeration to the new Windows USB backend.

device/usb/usb_service_win.h

Index: device/usb/usb_service_win.h
diff --git a/device/usb/usb_service_win.h b/device/usb/usb_service_win.h
index a6feb81a3e02d4e885cbb4cf48c073423a2ce95d..a91557786ecfc19c9f3d35d57036ea3ab0ca37be 100644
--- a/device/usb/usb_service_win.h
+++ b/device/usb/usb_service_win.h
@@ -4,17 +4,63 @@
 
 #include "device/usb/usb_service.h"
 
+#include <list>
+#include <unordered_map>
+
 #include "base/macros.h"
+#include "base/memory/weak_ptr.h"
+#include "base/scoped_observer.h"
+#include "device/base/device_monitor_win.h"
+#include "device/usb/usb_device_win.h"
+
+namespace base {
+class SequencedTaskRunner;
+}
 
 namespace device {
 
-class UsbServiceWin : public UsbService {
+class UsbServiceWin : public DeviceMonitorWin::Observer, public UsbService {
  public:
   explicit UsbServiceWin(
       scoped_refptr<base::SequencedTaskRunner> blocking_task_runner);
   ~UsbServiceWin() override;
 
  private:
+  class BlockingThreadHelper;
+
+  // device::UsbService implementation
+  void GetDevices(const GetDevicesCallback& callback) override;
+
+  // device::DeviceMonitorWin::Observer implementation
+  void OnDeviceAdded(const GUID& class_guid,
+                     const std::string& device_path) override;
+  void OnDeviceRemoved(const GUID& class_guid,
+                       const std::string& device_path) override;
+
+  // Methods called by BlockingThreadHelper
+  void HelperStarted();
+  void CreateDeviceObject(const std::string& device_path,
+                          const std::string& hub_path,
+                          int port_number);
+
+  void DeviceReady(scoped_refptr<UsbDeviceWin> device, bool success);
+
+  bool enumeration_ready() {
+    return helper_started_ && first_enumeration_countdown_ == 0;
+  }
+
+  // Enumeration callbacks are queued until an enumeration completes.
+  bool helper_started_ = false;
+  uint32_t first_enumeration_countdown_ = 0;
+  std::list<GetDevicesCallback> enumeration_callbacks_;
+
+  BlockingThreadHelper* helper_;
+  std::unordered_map<std::string, scoped_refptr<UsbDeviceWin>> devices_by_path_;
+
+  ScopedObserver<DeviceMonitorWin, DeviceMonitorWin::Observer> device_observer_;
+
+  base::WeakPtrFactory<UsbServiceWin> weak_factory_;
+
   DISALLOW_COPY_AND_ASSIGN(UsbServiceWin);
 };