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

media/base/video_frame.cc

Index: media/base/video_frame.cc
diff --git a/media/base/video_frame.cc b/media/base/video_frame.cc
index fc977364417280706f5dadd95ad58d47b299408e..b1cedc208b72aac548184a899bee9b360eaac938 100644
--- a/media/base/video_frame.cc
+++ b/media/base/video_frame.cc
@@ -206,13 +206,21 @@ int VideoFrame::stride(size_t plane) const {
 int VideoFrame::row_bytes(size_t plane) const {
   DCHECK(IsValidPlane(plane));
   switch (format_) {
+    // 16bpp.
     case RGB555:
     case RGB565:
+      return width_ * 2;
+
+    // 24bpp.
     case RGB24:
+      return width_ * 3;
+
+    // 32bpp.
     case RGB32:
     case RGBA:
-      return width_;
+      return width_ * 4;
 
+    // Planar, 8bpp.
     case YV12:
     case YV16:
       if (plane == kYPlane)