Boost thread priority while loading COM VideoCapture

The thread priority boost need to be apply at each call.

This is a follow up on:
  https://chromium-review.googlesource.com/c/chromium/src/+/2378395


Noticed in b93726646e382c66
The crash shows that the SCOPED_MAY_LOAD_LIBRARY_AT_BACKGROUND_PRIORITY()
already got called. The thread is still at a background priority and
it is loading a DLL.

R=joenotcharles@chromium.org,guidou@chromium.org

Bug: 973868
Change-Id: Ib4f0eaf317b8b6408f1f4ede8607ff00c1b5cc5b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2402163Reviewed-by: Joe Mason <joenotcharles@chromium.org>
Reviewed-by: Guido Urdaneta <guidou@chromium.org>
Commit-Queue: Etienne Bergeron <etienneb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#805527}

media/capture/video/win/video_capture_device_factory_win.cc

@@ -457,7 +457,7 @@ bool VideoCaptureDeviceFactoryWin::CreateDeviceFilterDirectShow(
 
   // Mitigate the issues caused by loading DLLs on a background thread
   // (http://crbug/973868).
-  SCOPED_MAY_LOAD_LIBRARY_AT_BACKGROUND_PRIORITY();
+  SCOPED_MAY_LOAD_LIBRARY_AT_BACKGROUND_PRIORITY_REPEATEDLY();
 
   HRESULT hr = moniker->BindToObject(0, 0, IID_PPV_ARGS(capture_filter));
   if (FAILED(hr)) {