Fix Gn Untracked headers in webrtc/modules/video_coding.

Fixed following headers in this CL
===================================

src/webrtc/modules/video_coding/sequence_number_util.h
src/webrtc/modules/video_coding/codecs/interface/common_constants.h
src/webrtc/modules/video_coding/codecs/interface/mock/mock_video_codec_interface.h

src/webrtc/modules/video_coding/codecs/vp8/include/vp8_globals.h
src/webrtc/modules/video_coding/codecs/vp9/include/vp9_globals.h
src/webrtc/modules/video_coding/codecs/h264/include/h264_globals.h

src/webrtc/modules/video_coding/utility/mock/mock_frame_dropper.h

src/webrtc/modules/video_coding/test/test_util.h
src/webrtc/modules/video_coding/codecs/interface/video_error_codes.h
src/webrtc/modules/video_coding/codecs/interface/video_codec_interface.h
src/webrtc/modules/video_coding/include/mock/mock_video_codec_interface.h

Remaining:
===========
src/webrtc/modules/video_coding/include/video_codec_interface.h
src/webrtc/modules/video_coding/include/video_error_codes.h

BUG=webrtc:7620

Review-Url: https://codereview.webrtc.org/3012323002
Cr-Commit-Position: refs/heads/master@{#19886}
diff --git a/media/BUILD.gn b/media/BUILD.gn
index e226087..4b956c8 100644
--- a/media/BUILD.gn
+++ b/media/BUILD.gn
@@ -134,7 +134,9 @@
 rtc_static_library("rtc_audio_video") {
   defines = []
   libs = []
-  deps = []
+  deps = [
+    "../modules/video_coding:video_coding_utility",
+  ]
   sources = [
     "engine/adm_helpers.cc",
     "engine/adm_helpers.h",
@@ -337,6 +339,7 @@
       "../modules/audio_coding:rent_a_codec",
       "../modules/audio_processing:audio_processing",
       "../modules/rtp_rtcp:rtp_rtcp",
+      "../modules/video_coding:video_coding_utility",
       "../p2p:rtc_p2p",
     ]
     sources = [