V4L2VDA: use YV12 as output format if processor supports it.

media/gpu/v4l2_video_decode_accelerator.cc

Index: media/gpu/v4l2_video_decode_accelerator.cc
diff --git a/media/gpu/v4l2_video_decode_accelerator.cc b/media/gpu/v4l2_video_decode_accelerator.cc
index 01e650a2f3cf35fdb5581f672b957672d9a2ae06..33e635cfd76211958aca43809a72339f60977683 100644
--- a/media/gpu/v4l2_video_decode_accelerator.cc
+++ b/media/gpu/v4l2_video_decode_accelerator.cc
@@ -2038,9 +2038,18 @@ uint32_t V4L2VideoDecodeAccelerator::FindImageProcessorInputFormat() {
 }
 
 uint32_t V4L2VideoDecodeAccelerator::FindImageProcessorOutputFormat() {
+  const uint32_t kPreferredEGLImageFormat = V4L2_PIX_FMT_YVU420;

[kcwu, 2016/08/19 06:27:33]

could you add comment here or in commit log, why this format is preferred?

[wuchengli, 2016/08/21 08:14:42]

Done.

   V4L2ImageProcessor image_processor(image_processor_device_);
   std::vector<uint32_t> processor_output_formats =
       image_processor.GetSupportedOutputFormats();
+
+  // Move the preferred format to the front.
+  std::vector<uint32_t>::iterator it =

[kcwu, 2016/08/19 06:27:33]

how about use "auto" type?

[wuchengli, 2016/08/21 08:14:42]

Done.

+      std::find(processor_output_formats.begin(),
+                processor_output_formats.end(), kPreferredEGLImageFormat);
+  if (it != processor_output_formats.end())
+    std::iter_swap(it, processor_output_formats.begin());
+
   for (uint32_t processor_output_format : processor_output_formats) {
     if (device_->CanCreateEGLImageFrom(processor_output_format)) {
       DVLOGF(1) << "Image processor output format=" << processor_output_format;