media/gpu/test: Add extra command line options to video decoder tests.

This CL adds extra command line options to the video_decode_accelerator_tests to
control the format and amount of video frames saved to disk when --output_frames
is specified:
--output_format: allows switching the file format between png and yuv.
--output_limit: allows putting a limit on the number of frames saved to disk.

TEST=ran new VDA tests on caroline

BUG=962354

Change-Id: Ifc0556986b28309b79ac7df9597154b85f08cc29
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1831728
Commit-Queue: David Staessens <[email protected]>
Reviewed-by: Hirokazu Honda <[email protected]>
Cr-Commit-Position: refs/heads/master@{#702728}
diff --git a/docs/media/gpu/video_decoder_test_usage.md b/docs/media/gpu/video_decoder_test_usage.md
index 81675a0..cb641b6d 100644
--- a/docs/media/gpu/video_decoder_test_usage.md
+++ b/docs/media/gpu/video_decoder_test_usage.md
@@ -66,14 +66,19 @@
      -v                  enable verbose mode, e.g. -v=2.
     --vmodule            enable verbose mode for the specified module,
                          e.g. --vmodule=*media/gpu*=2.
+
     --disable_validator  disable frame validation.
-    --output_frames      write the selected video frames to disk, possible
-                         values are "all|corrupt", the default output folder
-                         is "<testname>".
-    --output_folder      overwrite the default output folder used when
-                         "--output_frames" is specified.
     --use_vd             use the new VD-based video decoders, instead of
                          the default VDA-based video decoders.
+
+    --output_frames      write the selected video frames to disk, possible
+                         values are "all|corrupt".
+    --output_format      set the format of frames saved to disk, supported
+                         formats are "png" (default) and "yuv".
+    --output_limit       limit the number of frames saved to disk.
+    --output_folder      set the folder used to store frames, defaults to
+                         "<testname>"
+
     --gtest_help         display the gtest help and exit.
     --help               display this help and exit.