Revert "SeqNumUnwrapper::Unwrap now returns int64_t instead of uint64_t."

This reverts commit b0f968a761b715da4cf81e4b9c3cab0ccd322cf2.

Reason for revert: Need to update DecodedFramesHistory to manage negative picture IDs.

Original change's description:
> SeqNumUnwrapper::Unwrap now returns int64_t instead of uint64_t.
> 
> Bug: webrtc:10263
> Change-Id: Idaeae6be01bd4eba0691226c958d70e114161ffd
> Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/127295
> Commit-Queue: Philip Eliasson <philipel@webrtc.org>
> Reviewed-by: Johannes Kron <kron@webrtc.org>
> Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
> Cr-Commit-Position: refs/heads/master@{#27129}

TBR=kwiberg@webrtc.org,eladalon@webrtc.org,terelius@webrtc.org,philipel@webrtc.org,kron@webrtc.org

Change-Id: I529bb0475bd21a80fa244278aff1fd912a85c169
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: webrtc:10263
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/127885
Reviewed-by: Philip Eliasson <philipel@webrtc.org>
Commit-Queue: Philip Eliasson <philipel@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#27135}
diff --git a/modules/video_coding/loss_notification_controller.h b/modules/video_coding/loss_notification_controller.h
index 4cdfbb8..a2d640f 100644
--- a/modules/video_coding/loss_notification_controller.h
+++ b/modules/video_coding/loss_notification_controller.h
@@ -41,7 +41,7 @@
   void DiscardOldInformation();
 
   bool AllDependenciesDecodable(
-      int64_t unwrapped_frame_id,
+      uint64_t unwrapped_frame_id,
       rtc::ArrayView<const uint16_t> frame_dependency_diffs) const;
 
   // When the loss of a packet or the non-decodability of a frame is detected,
@@ -70,7 +70,7 @@
       RTC_GUARDED_BY(sequenced_task_checker_);
 
   // Tracked to avoid processing repeated frames (buggy/malicious remote).
-  absl::optional<int64_t> last_received_unwrapped_frame_id_
+  absl::optional<uint64_t> last_received_unwrapped_frame_id_
       RTC_GUARDED_BY(sequenced_task_checker_);
 
   // Tracked to avoid processing repeated packets.
@@ -97,7 +97,7 @@
   // Track which frames are decodable. Later frames are also decodable if
   // all of their dependencies can be found in this container.
   // (Naturally, later frames must also be assemblable to be decodable.)
-  std::set<int64_t> decodable_unwrapped_frame_ids_
+  std::set<uint64_t> decodable_unwrapped_frame_ids_
       RTC_GUARDED_BY(sequenced_task_checker_);
 
   rtc::SequencedTaskChecker sequenced_task_checker_;