Add Metronome to PC dependencies

This will enable Chrome to inject its metronome for use in WebRTC for
tasks like synchronized decoding.

Bug: webrtc:13560, chromium:1253787
Change-Id: I2488d746f57152a32d3adf92a3cdfdfdb8000c06
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/249381
Reviewed-by: Henrik Boström <hbos@webrtc.org>
Reviewed-by: Tomas Gunnarsson <tommi@webrtc.org>
Reviewed-by: Harald Alvestrand <hta@webrtc.org>
Commit-Queue: Evan Shrubsole <eshr@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#35853}

api/BUILD.gn

@@ -190,6 +190,7 @@ rtc_library("libjingle_peerconnection_api") {
     "crypto:frame_decryptor_interface",
     "crypto:frame_encryptor_interface",
     "crypto:options",
+    "metronome",
     "neteq:neteq_api",
     "rtc_event_log",
     "task_queue",

api/peer_connection_interface.h

@@ -95,6 +95,7 @@
 #include "api/jsep.h"
 #include "api/media_stream_interface.h"
 #include "api/media_types.h"
+#include "api/metronome/metronome.h"
 #include "api/neteq/neteq_factory.h"
 #include "api/network_state_predictor.h"
 #include "api/packet_socket_factory.h"
@@ -1410,6 +1411,7 @@ struct RTC_EXPORT PeerConnectionDependencies final {
   std::unique_ptr<rtc::SSLCertificateVerifier> tls_cert_verifier;
   std::unique_ptr<webrtc::VideoBitrateAllocatorFactory>
       video_bitrate_allocator_factory;
+  std::unique_ptr<webrtc::Metronome> metronome_;
 };
 
 // PeerConnectionFactoryDependencies holds all of the PeerConnectionFactory