When stopping QTKit video capture, call stopRunning before removeInput:.

media/video/capture/mac/video_capture_device_qtkit_mac.mm

Index: media/video/capture/mac/video_capture_device_qtkit_mac.mm
diff --git a/media/video/capture/mac/video_capture_device_qtkit_mac.mm b/media/video/capture/mac/video_capture_device_qtkit_mac.mm
index cd9c6d333e9dd36d9024d6e292ea0f7dc96c3781..79f8a100b95ba9a65d74bc5e4146f086f5fcedcc 100644
--- a/media/video/capture/mac/video_capture_device_qtkit_mac.mm
+++ b/media/video/capture/mac/video_capture_device_qtkit_mac.mm
@@ -219,8 +219,10 @@
 
 - (void)stopCapture {
   if ([[captureSession_ inputs] count] == 1) {
-    [captureSession_ removeInput:captureDeviceInput_];
+    // |stopRunning| must be called before |removeInput:| to avoid a deadlock
+    // with device enumeration when the active camera is unplugged.
     [captureSession_ stopRunning];
+    [captureSession_ removeInput:captureDeviceInput_];
   }
 
   [[NSNotificationCenter defaultCenter] removeObserver:self];