media/gpu/test: Update video decoder (perf) test usage documentation.

This CL updates the video_decoder_(perf_)tests usage documentation with
the additional "--use_vd_vda" parameter that was added recently.

BUG=None
TEST=checked doc in gitiles

Change-Id: I175ba21fe3563d092409a3202c7257dae90d520a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2215394Reviewed-by: Chih-Yu Huang <akahuang@chromium.org>
Commit-Queue: David Staessens <dstaessens@chromium.org>
Cr-Commit-Position: refs/heads/master@{#772116}

docs/media/gpu/video_decoder_perf_test_usage.md

@@ -92,6 +92,10 @@ Multiple command line arguments can be given to the command:
                          will be stored in the current working directory.
     --use_vd             use the new VD-based video decoders, instead of
                          the default VDA-based video decoders.
+    --use_vd_vda         use the new VD-based video decoders with a wrapper
+                         that translates to the VDA interface, used to test
+                         interaction with older components expecting the VDA
+                         interface.
     --gtest_help         display the gtest help and exit.
     --help               display this help and exit.
 

docs/media/gpu/video_decoder_test_usage.md

@@ -65,6 +65,10 @@ Multiple command line arguments can be given to the command:
     --disable_validator  disable frame validation.
     --use_vd             use the new VD-based video decoders, instead of
                          the default VDA-based video decoders.
+    --use_vd_vda         use the new VD-based video decoders with a wrapper
+                         that translates to the VDA interface, used to test
+                         interaction with older components expecting the VDA
+                         interface.
 
     --output_frames      write the selected video frames to disk, possible
                          values are "all|corrupt".