video_VideoDecodeAccelerator: set resultsdir for writing thumbnail image

While thumbnail test fails, write thumbnail image to results directory
so that it will be accessible to host and packed along with test logs.

BUG=chromium:701232
TEST=run autotest video_VideoDecodeAccelerator.

Change-Id: Icb6c896da7c51d9086af44abeed59f2a62f039e5
Reviewed-on: https://chromium-review.googlesource.com/461702
Commit-Ready: Pin-chih Lin <johnylin@chromium.org>
Tested-by: Pin-chih Lin <johnylin@chromium.org>
Reviewed-by: Owen Lin <owenlin@chromium.org>
diff --git a/client/site_tests/video_VideoDecodeAccelerator/video_VideoDecodeAccelerator.py b/client/site_tests/video_VideoDecodeAccelerator/video_VideoDecodeAccelerator.py
index aa48492..b559036 100644
--- a/client/site_tests/video_VideoDecodeAccelerator/video_VideoDecodeAccelerator.py
+++ b/client/site_tests/video_VideoDecodeAccelerator/video_VideoDecodeAccelerator.py
@@ -40,6 +40,11 @@
         for video in videos:
             cmd_line = ('--test_video_data="%s%s"' % (path, video))
 
+            # While thumbnail test fails, write thumbnail image to results
+            # directory so that it will be accessible to host and packed
+            # along with test logs.
+            cmd_line += (' --thumbnail_output_dir="%s"' % self.resultsdir)
+
             if utils.is_freon():
                 cmd_line += ' --ozone-platform=gbm'