Adding third_party/openh264 build files for encoding

BUILD.gn

Index: BUILD.gn
diff --git a/BUILD.gn b/BUILD.gn
index f58231fc4d16d6b9cdbed524e920c349566a2ae1..11fdfa236788e88c4a7c3b3be206f9cffe5f4bfc 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -13,6 +13,7 @@ import("//build/config/sanitizers/sanitizers.gni")
 import("//build/config/ui.gni")
 import("//build_overrides/v8.gni")
 import("//media/media_options.gni")
+import("//third_party/openh264/openh264_args.gni")
 
 if (is_android) {
   import("//build/config/android/config.gni")
@@ -586,6 +587,15 @@ group("both_gn_and_gyp") {
   if (is_chromecast) {
     deps += [ "//chromecast:cast_shell" ]
   }
+
+  if (use_openh264) {
+    deps += [
+      "//third_party/openh264:openh264_common",
+      "//third_party/openh264:openh264_processing",
+      "//third_party/openh264:openh264_encoder",
+      "//third_party/openh264:openh264_decoder",
+    ]
+  }
 }
 
 group("gn_only") {