Move device/usb classes from the FILE thread to UI thread.

device/test/usb_test_gadget.h

Index: device/test/usb_test_gadget.h
diff --git a/device/test/usb_test_gadget.h b/device/test/usb_test_gadget.h
index 99110a1966ed640108b164f910b8014ef5055aec..b1a8642c9a5ea6626324e824038293c5cd130bca 100644
--- a/device/test/usb_test_gadget.h
+++ b/device/test/usb_test_gadget.h
@@ -8,8 +8,13 @@
 #include <string>
 
 #include "base/macros.h"
+#include "base/memory/ref_counted.h"
 #include "base/memory/scoped_ptr.h"
 
+namespace base {
+class SingleThreadTaskRunner;
+}
+
 namespace device {
 
 class UsbDevice;
@@ -27,7 +32,8 @@ class UsbTestGadget {
   virtual ~UsbTestGadget() {}
 
   static bool IsTestEnabled();
-  static scoped_ptr<UsbTestGadget> Claim();
+  static scoped_ptr<UsbTestGadget> Claim(
+      scoped_refptr<base::SingleThreadTaskRunner> io_task_runner);
 
   virtual bool Unclaim() = 0;
   virtual bool Disconnect() = 0;
@@ -35,7 +41,6 @@ class UsbTestGadget {
   virtual bool SetType(Type type) = 0;
 
   virtual UsbDevice* GetDevice() const = 0;
-  virtual const std::string& GetSerialNumber() const = 0;
 
  protected:
   UsbTestGadget() {}