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 = [
diff --git a/modules/BUILD.gn b/modules/BUILD.gn
index 7a3ea2a..7394724 100644
--- a/modules/BUILD.gn
+++ b/modules/BUILD.gn
@@ -39,6 +39,7 @@
     "../api:optional",
     "../api:video_frame_api",
     "../rtc_base:rtc_base_approved",
+    "video_coding:codec_globals_headers",
   ]
 }
 
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",
     ]
diff --git a/modules/video_coding/BUILD.gn b/modules/video_coding/BUILD.gn
index 985002b..2371d08 100644
--- a/modules/video_coding/BUILD.gn
+++ b/modules/video_coding/BUILD.gn
@@ -111,8 +111,33 @@
   ]
 }
 
-rtc_static_library("video_coding_utility") {
+rtc_source_set("mock_headers") {
+  testonly = true
   sources = [
+    "codecs/interface/mock/mock_video_codec_interface.h",
+    "include/mock/mock_video_codec_interface.h",
+  ]
+  deps = [
+    ":video_coding_utility",
+    "../..:webrtc_common",
+    "../../test:test_support",
+  ]
+}
+
+rtc_source_set("codec_globals_headers") {
+  sources = [
+    "codecs/h264/include/h264_globals.h",
+    "codecs/interface/common_constants.h",
+    "codecs/vp8/include/vp8_globals.h",
+    "codecs/vp9/include/vp9_globals.h",
+  ]
+}
+
+rtc_source_set("video_coding_utility") {
+  sources = [
+    "codecs/interface/video_codec_interface.h",
+    "codecs/interface/video_error_codes.h",
+    "sequence_number_util.h",
     "utility/default_video_bitrate_allocator.cc",
     "utility/default_video_bitrate_allocator.h",
     "utility/frame_dropper.cc",
@@ -200,6 +225,7 @@
   }
 
   deps = [
+    ":video_coding_utility",
     "../..:webrtc_common",
     "../../common_video:common_video",
     "../../rtc_base:rtc_base_approved",
@@ -319,6 +345,7 @@
     }
 
     deps = [
+      ":mock_headers",
       ":video_coding",
       ":webrtc_vp8",
       "../../api:video_frame_api",
@@ -491,10 +518,12 @@
       "session_info_unittest.cc",
       "test/stream_generator.cc",
       "test/stream_generator.h",
+      "test/test_util.h",
       "timing_unittest.cc",
       "utility/default_video_bitrate_allocator_unittest.cc",
       "utility/frame_dropper_unittest.cc",
       "utility/ivf_file_writer_unittest.cc",
+      "utility/mock/mock_frame_dropper.h",
       "utility/moving_average_unittest.cc",
       "utility/quality_scaler_unittest.cc",
       "utility/simulcast_rate_allocator_unittest.cc",
@@ -510,6 +539,7 @@
       sources += [ "codecs/h264/h264_encoder_impl_unittest.cc" ]
     }
     deps = [
+      ":mock_headers",
       ":simulcast_test_utility",
       ":video_codecs_test_framework",
       ":video_coding",
diff --git a/sdk/android/BUILD.gn b/sdk/android/BUILD.gn
index ab9bfb6..de3c3c9 100644
--- a/sdk/android/BUILD.gn
+++ b/sdk/android/BUILD.gn
@@ -151,6 +151,7 @@
     "../../media:rtc_media_base",
     "../../modules:module_api",
     "../../modules/utility:utility",
+    "../../modules/video_coding:codec_globals_headers",
     "../../modules/video_coding:video_coding_utility",
     "../../rtc_base:rtc_base",
     "../../rtc_base:rtc_base_approved",
diff --git a/test/BUILD.gn b/test/BUILD.gn
index f603733..36f3539 100644
--- a/test/BUILD.gn
+++ b/test/BUILD.gn
@@ -571,6 +571,7 @@
     "../modules/audio_processing",
     "../modules/rtp_rtcp",
     "../modules/rtp_rtcp:mock_rtp_rtcp",
+    "../modules/video_coding:video_coding_utility",
     "../modules/video_coding:webrtc_h264",
     "../modules/video_coding:webrtc_vp8",
     "../modules/video_coding:webrtc_vp9",