VideoCaptureFormat: add method to print out pixel format as string

media/video/capture/video_capture_types.h

Index: media/video/capture/video_capture_types.h
diff --git a/media/video/capture/video_capture_types.h b/media/video/capture/video_capture_types.h
index 5f23a1b1760187f0c9b7e321f26fa2798cf80e41..a6a13a81b070cb33224012525bda8b8dc1911c18 100644
--- a/media/video/capture/video_capture_types.h
+++ b/media/video/capture/video_capture_types.h
@@ -46,6 +46,8 @@ class MEDIA_EXPORT VideoCaptureFormat {
                      float frame_rate,
                      VideoPixelFormat pixel_format);
 
+  static std::string PixelFormatToString(VideoPixelFormat format);
+
   // Checks that all values are in the expected range. All limits are specified
   // in media::Limits.
   bool IsValid() const;