Introduce DecodedFramesHistory class and use it in FrameBuffer

This is a space efficient way to store more records about decoded frames,
which is needed for long term references.

Bug: webrtc:9710
Change-Id: I051d59d34a966d48db011142466d9cd15304b7d9
Reviewed-on: https://webrtc-review.googlesource.com/c/116792
Commit-Queue: Ilya Nikolaevskiy <ilnik@webrtc.org>
Reviewed-by: Philip Eliasson <philipel@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#26240}

modules/video_coding/utility/decoded_frames_history.h

@@ -0,0 +1,60 @@
+/*
+ *  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.
+ */
+
+#ifndef MODULES_VIDEO_CODING_UTILITY_DECODED_FRAMES_HISTORY_H_
+#define MODULES_VIDEO_CODING_UTILITY_DECODED_FRAMES_HISTORY_H_
+
+#include <stdint.h>
+#include <bitset>
+#include <vector>
+
+#include "absl/types/optional.h"
+#include "api/video/encoded_frame.h"
+
+namespace webrtc {
+namespace video_coding {
+
+class DecodedFramesHistory {
+ public:
+  // window_size - how much frames back to the past are actually remembered.
+  explicit DecodedFramesHistory(size_t window_size);
+  ~DecodedFramesHistory();
+  // Called for each decoded frame. Assumes picture id's are non-decreasing.
+  void InsertDecoded(const VideoLayerFrameId& frameid, uint32_t timestamp);
+  // Query if the following (picture_id, spatial_id) pair was inserted before.
+  // Should be at most less by window_size-1 than the last inserted picture id.
+  bool WasDecoded(const VideoLayerFrameId& frameid);
+
+  void Clear();
+
+  absl::optional<VideoLayerFrameId> GetLastDecodedFrameId();
+  absl::optional<uint32_t> GetLastDecodedFrameTimestamp();
+
+ private:
+  struct LayerHistory {
+    LayerHistory();
+    ~LayerHistory();
+    // Cyclic bitset buffer. Stores last known |window_size| bits.
+    // last_stored_index is the last actually stored bit. Previous
+    // |window_size-1| bits are also in the memory. Value for i-th bit is at
+    // buffer[i % window_size].
+    std::vector<bool> buffer;
+    int64_t last_stored_index;
+  };
+
+  const int window_size_;
+  std::vector<LayerHistory> layers_;
+  absl::optional<VideoLayerFrameId> last_decoded_frame_;
+  absl::optional<uint32_t> last_decoded_frame_timestamp_;
+};
+
+}  // namespace video_coding
+}  // namespace webrtc
+#endif  // MODULES_VIDEO_CODING_UTILITY_DECODED_FRAMES_HISTORY_H_