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/common_video/BUILD.gn b/common_video/BUILD.gn
index 10a646f..ccb93ee 100644
--- a/common_video/BUILD.gn
+++ b/common_video/BUILD.gn
@@ -47,6 +47,7 @@
     "../api/video:video_bitrate_allocator",
     "../api/video:video_frame",
     "../api/video:video_frame_i420",
+    "../api/video:video_rtp_headers",
     "../api/video_codecs:bitstream_parser_api",
     "../media:rtc_h264_profile_id",
     "../rtc_base",
@@ -95,6 +96,7 @@
       "../api/video:video_frame",
       "../api/video:video_frame_i010",
       "../api/video:video_frame_i420",
+      "../api/video:video_rtp_headers",
       "../media:rtc_h264_profile_id",
       "../rtc_base",
       "../rtc_base:checks",