media/gpu/v4l2vd: Log modifier usage in decoder

Add a way to tell what modifier was used to
to allocate the decoded video buffers.

BUG=b:149525848
TEST=none

Change-Id: I94b16c90a32ca9e13c3752b1c9706dbf1d34b5f6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2569991
Auto-Submit: Fritz Koenig <frkoenig@chromium.org>
Reviewed-by: Alexandre Courbot <acourbot@chromium.org>
Commit-Queue: Fritz Koenig <frkoenig@chromium.org>
Cr-Commit-Position: refs/heads/master@{#836177}

media/gpu/v4l2/v4l2_video_decoder.cc

@@ -361,6 +361,7 @@ bool V4L2VideoDecoder::SetupOutputFormat(const gfx::Size& size,
       return false;
     }
 
+    VLOGF(1) << "buffer modifier: " << std::hex << layout->modifier();
     if (layout->modifier() &&
         layout->modifier() != gfx::NativePixmapHandle::kNoModifier) {
       base::Optional<struct v4l2_format> modifier_format =