gpu/mac: Fix video capture bug

Support for the current |best_fourcc| value of kCVPixelFormatType_422YpCbCr8
by FourCCToChromiumPixelFormat was removed in https://chromium-review.googlesource.com/c/chromium/src/+/1732895.
This change updates the |best_fourcc| to a supported format.

Bug: 1012204
Bug: 988538
Change-Id: I4cbff3bdf495806f7290bd2edf2c33cee5d67925
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1853864
Commit-Queue: Sasha McIntosh <sashamcintosh@chromium.org>
Reviewed-by: Guido Urdaneta <guidou@chromium.org>
Cr-Commit-Position: refs/heads/master@{#705613}

media/capture/video/mac/video_capture_device_avfoundation_mac.mm

@@ -344,7 +344,7 @@ void ExtractBaseAddressAndLength(char** base_address,
   frameHeight_ = height;
   frameRate_ = frameRate;
 
-  FourCharCode best_fourcc = kCVPixelFormatType_422YpCbCr8;
+  FourCharCode best_fourcc = kCMPixelFormat_422YpCbCr8_yuvs;
   const bool prefer_mjpeg =
       width > kMjpegWidthThreshold || height > kMjpegHeightThreshold;
   for (AVCaptureDeviceFormat* format in captureDevice_.formats) {