Use RunLoop, but do not call RunUntilIdle() multiple times

media/midi/midi_manager_usb_unittest.cc

Index: media/midi/midi_manager_usb_unittest.cc
diff --git a/media/midi/midi_manager_usb_unittest.cc b/media/midi/midi_manager_usb_unittest.cc
index dda6775af3652a785920f17c916154c271ecd5b4..978658826aeb8dab54faa7f347d2459dfc73c83d 100644
--- a/media/midi/midi_manager_usb_unittest.cc
+++ b/media/midi/midi_manager_usb_unittest.cc
@@ -179,9 +179,10 @@ class MidiManagerUsbTest : public ::testing::Test {
   void RunCallbackUntilCallbackInvoked(
       bool result, UsbMidiDevice::Devices* devices) {
     factory_->callback_.Run(result, devices);
-    base::RunLoop run_loop;
-    while (!client_->complete_start_session_)
+    while (!client_->complete_start_session_) {
+      base::RunLoop run_loop;
       run_loop.RunUntilIdle();
+    }
   }
 
   scoped_ptr<MidiManagerUsbForTesting> manager_;