Add untracked headers to video_coding.

This creates a new target for pure defines and interfaces. I think
that makes sense (though include/ makes it harder to see when .cc and
.h files should live together).

Bug: webrtc:7620
Change-Id: Ifb0f50faf99166202836c0446feed3443eb52c6e
Reviewed-on: https://webrtc-review.googlesource.com/34657
Commit-Queue: Patrik Höglund <phoglund@webrtc.org>
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#21516}
diff --git a/sdk/android/BUILD.gn b/sdk/android/BUILD.gn
index 302a43d..366961d 100644
--- a/sdk/android/BUILD.gn
+++ b/sdk/android/BUILD.gn
@@ -255,6 +255,7 @@
     "../../modules:module_api",
     "../../modules/utility:utility",
     "../../modules/video_coding:codec_globals_headers",
+    "../../modules/video_coding:video_codec_interface",
     "../../modules/video_coding:video_coding_utility",
     "../../modules/video_coding:webrtc_vp8",
     "../../modules/video_coding:webrtc_vp9",