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/modules/remote_bitrate_estimator/BUILD.gn b/modules/remote_bitrate_estimator/BUILD.gn
index 72e6f1d..d29969a 100644
--- a/modules/remote_bitrate_estimator/BUILD.gn
+++ b/modules/remote_bitrate_estimator/BUILD.gn
@@ -151,6 +151,7 @@
       "../congestion_controller",
       "../pacing",
       "../rtp_rtcp",
+      "../video_coding:video_coding_utility",
       "//testing/gmock",
       "//testing/gtest",
     ]