Migrate HidServiceLinux and HidConnectionLinux to BrowserThread::UI.

device/hid/hid_service_linux.h

Index: device/hid/hid_service_linux.h
diff --git a/device/hid/hid_service_linux.h b/device/hid/hid_service_linux.h
index 80239c4bdeae6ffe7df9969ab9f20eccdc966004..59b6036d8b83e0977c84a238e922bfdaf50e1ae8 100644
--- a/device/hid/hid_service_linux.h
+++ b/device/hid/hid_service_linux.h
@@ -8,40 +8,50 @@
 #include "base/compiler_specific.h"
 #include "base/macros.h"
 #include "base/memory/weak_ptr.h"
-#include "device/hid/device_monitor_linux.h"
 #include "device/hid/hid_device_info.h"
 #include "device/hid/hid_service.h"
 
-struct udev_device;
-
 namespace device {
 
 class HidConnection;
 
-class HidServiceLinux : public HidService,
-                        public DeviceMonitorLinux::Observer {
+class HidServiceLinux : public HidService {
  public:
   HidServiceLinux(scoped_refptr<base::SingleThreadTaskRunner> ui_task_runner);
 
   void Connect(const HidDeviceId& device_id,
                const ConnectCallback& callback) override;
 
-  // Implements DeviceMonitorLinux::Observer:
-  void OnDeviceAdded(udev_device* device) override;
-  void OnDeviceRemoved(udev_device* device) override;
-
  private:
+  struct ConnectParams;
+  class Helper;
+  friend class Helper;
+
   ~HidServiceLinux() override;
 
-  void FinishConnect(const HidDeviceId& device_id,
-                     const std::string device_node,
-                     const ConnectCallback& callback,
-                     bool success);
+  // Constructs this services helper object that lives on the FILE thread.
+  static void StartHelper(
+      base::WeakPtr<HidServiceLinux> weak_ptr,
+      scoped_refptr<base::SingleThreadTaskRunner> task_runner);
+
+  // These functions implement the process of locating, requesting access to and
+  // opening a device. Because this operation crosses multiple threads these
+  // functions are static and the necessary parameters are passed as a single
+  // struct.
+#if defined(OS_CHROMEOS)
+  static void OnRequestPathAccessComplete(scoped_ptr<ConnectParams> params,
+                                          bool success);
+#endif  // defined(OS_CHROMEOS)
+  static void OpenDevice(scoped_ptr<ConnectParams> params);
+  static void ConnectImpl(scoped_ptr<ConnectParams> params);
 
   scoped_refptr<base::SingleThreadTaskRunner> task_runner_;
-  scoped_refptr<base::SingleThreadTaskRunner> ui_task_runner_;
+  scoped_refptr<base::SingleThreadTaskRunner> file_task_runner_;
 
+  // The helper lives on the FILE thread and holds a weak reference back to the
+  // service that owns it.
   base::WeakPtrFactory<HidServiceLinux> weak_factory_;
+  scoped_ptr<Helper> helper_;
 
   DISALLOW_COPY_AND_ASSIGN(HidServiceLinux);
 };