Remove field-trial parameter to simulate a slow decoder

Clean up by removing unused field-trial that was added in this CL
https://webrtc-review.googlesource.com/c/src/+/151911
to make it possible to simulate a slow decoder.

Bug: None
Change-Id: I237f3ac6baae76f81fcd2938e43eab9c19cea45f
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/261681
Reviewed-by: Erik Språng <sprang@webrtc.org>
Commit-Queue: Johannes Kron <kron@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#36824}

modules/video_coding/generic_decoder.cc

@@ -19,7 +19,6 @@
 #include "modules/video_coding/include/video_error_codes.h"
 #include "rtc_base/checks.h"
 #include "rtc_base/logging.h"
-#include "rtc_base/thread.h"
 #include "rtc_base/time_utils.h"
 #include "rtc_base/trace_event.h"
 #include "system_wrappers/include/clock.h"
@@ -30,15 +29,9 @@ VCMDecodedFrameCallback::VCMDecodedFrameCallback(
     VCMTiming* timing,
     Clock* clock,
     const FieldTrialsView& field_trials)
-    : _clock(clock),
+    : _clock(clock), _timing(timing), _timestampMap(kDecoderFrameMemoryLength) {
-      _timing(timing),
-      _timestampMap(kDecoderFrameMemoryLength),
-      _extra_decode_time("t", absl::nullopt) {
   ntp_offset_ =
       _clock->CurrentNtpInMilliseconds() - _clock->TimeInMilliseconds();
-
-  ParseFieldTrial({&_extra_decode_time},
-                  field_trials.Lookup("WebRTC-SlowDownDecoder"));
 }
 
 VCMDecodedFrameCallback::~VCMDecodedFrameCallback() {}
@@ -76,11 +69,6 @@ int32_t VCMDecodedFrameCallback::Decoded(VideoFrame& decodedImage,
 void VCMDecodedFrameCallback::Decoded(VideoFrame& decodedImage,
                                       absl::optional<int32_t> decode_time_ms,
                                       absl::optional<uint8_t> qp) {
-  // Wait some extra time to simulate a slow decoder.
-  if (_extra_decode_time) {
-    rtc::Thread::SleepMs(_extra_decode_time->ms());
-  }
-
   RTC_DCHECK(_receiveCallback) << "Callback must not be null at this point";
   TRACE_EVENT_INSTANT1("webrtc", "VCMDecodedFrameCallback::Decoded",
                        "timestamp", decodedImage.timestamp());

modules/video_coding/generic_decoder.h

@@ -15,13 +15,11 @@
 
 #include "api/field_trials_view.h"
 #include "api/sequence_checker.h"
-#include "api/units/time_delta.h"
 #include "api/video_codecs/video_decoder.h"
 #include "modules/video_coding/encoded_frame.h"
 #include "modules/video_coding/include/video_codec_interface.h"
 #include "modules/video_coding/timestamp_map.h"
 #include "modules/video_coding/timing.h"
-#include "rtc_base/experiments/field_trial_parser.h"
 #include "rtc_base/synchronization/mutex.h"
 
 namespace webrtc {
@@ -64,8 +62,6 @@ class VCMDecodedFrameCallback : public DecodedImageCallback {
   Mutex lock_;
   VCMTimestampMap _timestampMap RTC_GUARDED_BY(lock_);
   int64_t ntp_offset_;
-  // Set by the field trial WebRTC-SlowDownDecoder to simulate a slow decoder.
-  FieldTrialOptional<TimeDelta> _extra_decode_time;
 };
 
 class VCMGenericDecoder {