Refactor webrtc/modules/utility for gn check

The now checked target is:
"//webrtc/modules/utility/*"

BUG=webrtc:6828
NOTRY=True

Review-Url: https://codereview.webrtc.org/2606483002
Cr-Commit-Position: refs/heads/master@{#15803}
diff --git a/.gn b/.gn
index c381566..14478ca 100644
--- a/.gn
+++ b/.gn
@@ -32,6 +32,7 @@
   "//webrtc/modules/media_file/*",
   "//webrtc/modules/pacing/*",
   "//webrtc/modules/rtp_rtcp/*",
+  "//webrtc/modules/utility/*",
   "//webrtc/modules/video_capture/*",
   "//webrtc/modules/video_coding/*",
   "//webrtc/stats:rtc_stats",
diff --git a/webrtc/modules/utility/BUILD.gn b/webrtc/modules/utility/BUILD.gn
index 5888304..edd428f 100644
--- a/webrtc/modules/utility/BUILD.gn
+++ b/webrtc/modules/utility/BUILD.gn
@@ -42,6 +42,7 @@
     "../../common_audio",
     "../../system_wrappers",
     "../audio_coding",
+    "../audio_coding:audio_format_conversion",
     "../audio_coding:builtin_audio_decoder_factory",
     "../audio_coding:rent_a_codec",
     "../media_file",