Rename test output to test artifacts.

On android, the flag to store the frame with the worst PSNR was called
'--test_artifacts_dir'.
I think test artifacts is a better name.

TBR=sprang@webrtc.org

Bug: chromium:745469
Change-Id: I358ea2985a1df2da12b81df173d74ac193556a49
Reviewed-on: https://webrtc-review.googlesource.com/4080
Commit-Queue: Edward Lemur <ehmaldonado@webrtc.org>
Reviewed-by: Henrik Kjellander <kjellander@webrtc.org>
Reviewed-by: Ilya Nikolaevskiy <ilnik@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#20000}
diff --git a/video/BUILD.gn b/video/BUILD.gn
index 16f6bd0..e0809b4 100644
--- a/video/BUILD.gn
+++ b/video/BUILD.gn
@@ -117,7 +117,7 @@
       "../test:test_renderer",
       "../test:test_renderer",
       "../test:test_support",
-      "../test:test_support_test_output",
+      "../test:test_support_test_artifacts",
       "../test:video_test_common",
       "../test:video_test_common",
       "../test:video_test_support",