Remove BrowserThread dependency from usb_service.

components/usb_service/usb_device_impl.h

Index: components/usb_service/usb_device_impl.h
diff --git a/components/usb_service/usb_device_impl.h b/components/usb_service/usb_device_impl.h
index e27a692853b1c6a740ff7566934a2e501e801103..07711bc2e54f3c6ba947424853bc7a8af58a168a 100644
--- a/components/usb_service/usb_device_impl.h
+++ b/components/usb_service/usb_device_impl.h
@@ -15,6 +15,10 @@
 struct libusb_device;
 struct libusb_config_descriptor;
 
+namespace base {
+class SingleThreadTaskRunner;
+}
+
 namespace usb_service {
 
 class UsbDeviceHandleImpl;
@@ -40,6 +44,7 @@ class UsbDeviceImpl : public UsbDevice {
 
   // Called by UsbServiceImpl only;
   UsbDeviceImpl(scoped_refptr<UsbContext> context,
+                scoped_refptr<base::SingleThreadTaskRunner> ui_task_runner,
                 PlatformUsbDevice platform_device,
                 uint16 vendor_id,
                 uint16 product_id,
@@ -61,6 +66,9 @@ class UsbDeviceImpl : public UsbDevice {
   typedef std::vector<scoped_refptr<UsbDeviceHandleImpl> > HandlesVector;
   HandlesVector handles_;
 
+  // Reference to the UI thread for permission-broker calls.
+  scoped_refptr<base::SingleThreadTaskRunner> ui_task_runner_;
+
   DISALLOW_COPY_AND_ASSIGN(UsbDeviceImpl);
 };