Fix incorrect VideoFrame::row_bytes() for RGB. Add tests.

media/base/video_frame.h

Index: media/base/video_frame.h
diff --git a/media/base/video_frame.h b/media/base/video_frame.h
index f65bf235bbfbbf31ea771860a1db0347d096ecfd..f2b838eb8983ec43d1d9a417341fe26f87e0b8a2 100644
--- a/media/base/video_frame.h
+++ b/media/base/video_frame.h
@@ -83,14 +83,14 @@ class MEDIA_EXPORT VideoFrame : public StreamSample {
 
   size_t height() const { return height_; }
 
-  int stride(size_t plane) const;
+  size_t stride(size_t plane) const;
 
   // Returns the number of bytes per row and number of rows for a given plane.
   //
   // As opposed to stride(), row_bytes() refers to the bytes representing
   // visible pixels.
-  int row_bytes(size_t plane) const;
-  int rows(size_t plane) const;
+  size_t row_bytes(size_t plane) const;
+  size_t rows(size_t plane) const;
 
   // Returns pointer to the buffer for a given plane. The memory is owned by
   // VideoFrame object and must not be freed by the caller.