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.cc

@@ -0,0 +1,58 @@
+/*
+ *  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.
+ */
+
+#include "modules/video_coding/timing/codec_timer.h"
+
+#include <cstdint>
+
+namespace webrtc {
+
+namespace {
+
+// The first kIgnoredSampleCount samples will be ignored.
+const int kIgnoredSampleCount = 5;
+// Return the `kPercentile` value in RequiredDecodeTimeMs().
+const float kPercentile = 0.95f;
+// The window size in ms.
+const int64_t kTimeLimitMs = 10000;
+
+}  // anonymous namespace
+
+CodecTimer::CodecTimer() : ignored_sample_count_(0), filter_(kPercentile) {}
+CodecTimer::~CodecTimer() = default;
+
+void CodecTimer::AddTiming(int64_t decode_time_ms, int64_t now_ms) {
+  // Ignore the first `kIgnoredSampleCount` samples.
+  if (ignored_sample_count_ < kIgnoredSampleCount) {
+    ++ignored_sample_count_;
+    return;
+  }
+
+  // Insert new decode time value.
+  filter_.Insert(decode_time_ms);
+  history_.emplace(decode_time_ms, now_ms);
+
+  // Pop old decode time values.
+  while (!history_.empty() &&
+         now_ms - history_.front().sample_time_ms > kTimeLimitMs) {
+    filter_.Erase(history_.front().decode_time_ms);
+    history_.pop();
+  }
+}
+
+// Get the 95th percentile observed decode time within a time window.
+int64_t CodecTimer::RequiredDecodeTimeMs() const {
+  return filter_.GetPercentileValue();
+}
+
+CodecTimer::Sample::Sample(int64_t decode_time_ms, int64_t sample_time_ms)
+    : decode_time_ms(decode_time_ms), sample_time_ms(sample_time_ms) {}
+
+}  // namespace webrtc