Split out counting unique rtp timestamps from packet_buffer

Bug: None
Change-Id: Ia6fd05f284e8304cf56ab9ddf944fb222a4c9573
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/158676
Reviewed-by: Ilya Nikolaevskiy <ilnik@webrtc.org>
Reviewed-by: Philip Eliasson <philipel@webrtc.org>
Commit-Queue: Danil Chapovalov <danilchap@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#29656}

modules/video_coding/unique_timestamp_counter.cc

@@ -0,0 +1,41 @@
+/*
+ *  Copyright (c) 2019 The WebRTC project authors. All Rights Reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+#include "modules/video_coding/unique_timestamp_counter.h"
+
+#include <cstdint>
+#include <memory>
+#include <set>
+
+namespace webrtc {
+namespace {
+
+constexpr int kMaxHistory = 1000;
+
+}  // namespace
+
+UniqueTimestampCounter::UniqueTimestampCounter()
+    : latest_(std::make_unique<uint32_t[]>(kMaxHistory)) {}
+
+void UniqueTimestampCounter::Add(uint32_t value) {
+  if (value == last_ || !search_index_.insert(value).second) {
+    // Already known.
+    return;
+  }
+  int index = unique_seen_ % kMaxHistory;
+  if (unique_seen_ >= kMaxHistory) {
+    search_index_.erase(latest_[index]);
+  }
+  latest_[index] = value;
+  last_ = value;
+  ++unique_seen_;
+}
+
+}  // namespace webrtc