Move sequence_number_utils.h to rtc_base/

Bug: webrtc:8440
Change-Id: I36e70da6ce70b95db7d3fce8b0013bff5c795bfc
Reviewed-on: https://webrtc-review.googlesource.com/14860
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Reviewed-by: Åsa Persson <asapersson@webrtc.org>
Reviewed-by: Philip Eliasson <philipel@webrtc.org>
Commit-Queue: Björn Terelius <terelius@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#20429}
diff --git a/modules/video_coding/frame_buffer2.h b/modules/video_coding/frame_buffer2.h
index e502666..f535442 100644
--- a/modules/video_coding/frame_buffer2.h
+++ b/modules/video_coding/frame_buffer2.h
@@ -19,10 +19,10 @@
 #include "modules/video_coding/frame_object.h"
 #include "modules/video_coding/include/video_coding_defines.h"
 #include "modules/video_coding/inter_frame_delay.h"
-#include "modules/video_coding/sequence_number_util.h"
 #include "rtc_base/constructormagic.h"
 #include "rtc_base/criticalsection.h"
 #include "rtc_base/event.h"
+#include "rtc_base/numerics/sequence_number_util.h"
 #include "rtc_base/thread_annotations.h"
 
 namespace webrtc {