Prepare for splitting the api/video:video_frames build rule.

This change is part of a change to break the dependency between "api:rtp_headers" and "api/video:video_frame". It does so by first creating an empty "api/video:video_rtp_headers" build rule so that downstream projects can be fixed before moving the source files.

Bug: webrtc:10668
Change-Id: I81aa6edfef3639b457a40aa93de048e62cbfd8ef
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/140291
Commit-Queue: Chen Xing <chxg@google.com>
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#28209}
diff --git a/call/BUILD.gn b/call/BUILD.gn
index 52f13da..9ee0520 100644
--- a/call/BUILD.gn
+++ b/call/BUILD.gn
@@ -136,6 +136,7 @@
     "../api/units:time_delta",
     "../api/units:timestamp",
     "../api/video:video_frame",
+    "../api/video:video_rtp_headers",
     "../api/video_codecs:video_codecs_api",
     "../logging:rtc_event_bwe",
     "../logging:rtc_event_log_api",
@@ -276,6 +277,7 @@
     "../api:rtp_headers",
     "../api:transport_api",
     "../api/video:video_frame",
+    "../api/video:video_rtp_headers",
     "../api/video:video_stream_encoder",
     "../api/video_codecs:video_codecs_api",
     "../common_video",
@@ -374,6 +376,7 @@
       "../api/audio_codecs:builtin_audio_decoder_factory",
       "../api/task_queue:default_task_queue_factory",
       "../api/video:video_frame",
+      "../api/video:video_rtp_headers",
       "../audio",
       "../logging:rtc_event_log_api",
       "../logging:rtc_event_log_impl_base",