Replace uses of raw uint32's with a type-checked RtpTimeTicks data type.

media/cast/sender/video_sender.h

Index: media/cast/sender/video_sender.h
diff --git a/media/cast/sender/video_sender.h b/media/cast/sender/video_sender.h
index ab31e7b9b3562185474864c02c47a591fff15780..eee4da5c266348cd2f26b8c7a53d4344e49d8c12 100644
--- a/media/cast/sender/video_sender.h
+++ b/media/cast/sender/video_sender.h
@@ -14,6 +14,7 @@
 #include "base/time/time.h"
 #include "media/cast/cast_config.h"
 #include "media/cast/cast_sender.h"
+#include "media/cast/common/rtp_time.h"
 #include "media/cast/sender/congestion_control.h"
 #include "media/cast/sender/frame_sender.h"
 
@@ -89,7 +90,7 @@ class VideoSender : public FrameSender,
   base::TimeDelta duration_in_encoder_;
 
   // The timestamp of the frame that was last enqueued in |video_encoder_|.
-  RtpTimestamp last_enqueued_frame_rtp_timestamp_;
+  RtpTimeTicks last_enqueued_frame_rtp_timestamp_;
   base::TimeTicks last_enqueued_frame_reference_time_;
 
   // Remember what we set the bitrate to before, no need to set it again if