Video capture: Refactor GetBestMatchedFormat from Win to OS independent

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 ec57c451372831580b5476befa53d4acf6398982..e2bb937ac36d4068b90b01852a5225482f48a59e 100644
--- a/media/video/capture/video_capture_types.h
+++ b/media/video/capture/video_capture_types.h
@@ -92,6 +92,12 @@ class MEDIA_EXPORT VideoCaptureParams {
   ResolutionChangePolicy resolution_change_policy;
 };
 
+// Helper function to compare video capture formats when finding the most
+// closely matched video format given a requested video format.
+// Smaller difference means more closely matched formats.
+int DiffVideoCaptureFormat(const VideoCaptureFormat& lhs,
+                           const VideoCaptureFormat& rhs);
+
 }  // namespace media
 
 #endif  // MEDIA_VIDEO_CAPTURE_VIDEO_CAPTURE_TYPES_H_