Refactor webrtc/modules/media_file for GN check

This moves some GN check configurations out of .gn to individual
targets.

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

BUG=webrtc:6828
NOTRY=True

Review-Url: https://codereview.webrtc.org/2593693002
Cr-Commit-Position: refs/heads/master@{#15726}
diff --git a/.gn b/.gn
index 7849e32..d391a53 100644
--- a/.gn
+++ b/.gn
@@ -29,6 +29,7 @@
   "//webrtc/modules/audio_mixer/*",
   "//webrtc/modules/audio_processing/*",
   "//webrtc/modules/desktop_capture/*",
+  "//webrtc/modules/media_file/*",
   "//webrtc/modules/video_capture/*",
   "//webrtc/modules/video_coding/*",
   "//webrtc/stats:rtc_stats",
diff --git a/webrtc/modules/media_file/BUILD.gn b/webrtc/modules/media_file/BUILD.gn
index 37e966d..f4e93c9 100644
--- a/webrtc/modules/media_file/BUILD.gn
+++ b/webrtc/modules/media_file/BUILD.gn
@@ -34,6 +34,7 @@
 
   deps = [
     "../..:webrtc_common",
+    "../../base:rtc_base_approved",
     "../../common_audio",
     "../../system_wrappers",
   ]