Start moving timing helper classes into timing/ sub-folder.

Putting these classes in a sub folder increases
structure and clarifies that they are used as
helper classes. Affected classes in this change:
  * CodecTimer
  * InterFrameDelay
  * RttFilter
VCMTiming will be moved in a separate CL.

Additional changes:
  * Remove VCM prefix from class names.
  * Introduce granular BUILD.gn targets.
  * Update some includes.

Bug: webrtc:14111
Change-Id: Ia75128aa955a819033b97d4784cb61904de7230b
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/262960
Commit-Queue: Rasmus Brandt <brandtr@webrtc.org>
Reviewed-by: Tomas Gunnarsson <tommi@webrtc.org>
Reviewed-by: Åsa Persson <asapersson@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#36975}

modules/video_coding/timing/codec_timer.h

@@ -0,0 +1,50 @@
+/*
+ *  Copyright (c) 2011 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_TIMING_CODEC_TIMER_H_
+#define MODULES_VIDEO_CODING_TIMING_CODEC_TIMER_H_
+
+#include <queue>
+
+#include "rtc_base/numerics/percentile_filter.h"
+
+namespace webrtc {
+
+class CodecTimer {
+ public:
+  CodecTimer();
+  ~CodecTimer();
+
+  // Add a new decode time to the filter.
+  void AddTiming(int64_t new_decode_time_ms, int64_t now_ms);
+
+  // Get the required decode time in ms. It is the 95th percentile observed
+  // decode time within a time window.
+  int64_t RequiredDecodeTimeMs() const;
+
+ private:
+  struct Sample {
+    Sample(int64_t decode_time_ms, int64_t sample_time_ms);
+    int64_t decode_time_ms;
+    int64_t sample_time_ms;
+  };
+
+  // The number of samples ignored so far.
+  int ignored_sample_count_;
+  // Queue with history of latest decode time values.
+  std::queue<Sample> history_;
+  // `filter_` contains the same values as `history_`, but in a data structure
+  // that allows efficient retrieval of the percentile value.
+  PercentileFilter<int64_t> filter_;
+};
+
+}  // namespace webrtc
+
+#endif  // MODULES_VIDEO_CODING_TIMING_CODEC_TIMER_H_