Revert of Remove ignored return code from modules. (patchset #3 id:40001 of https://codereview.webrtc.org/1703833002/ )

Reason for revert:
Breaks Chromium.

Original issue's description:
> Remove ignored return code from modules.
>
> ModuleProcessImpl doesn't act on return codes and having them around is
> confusing (it's unclear what an error return code here would do even).
>
> BUG=
> R=tommi@webrtc.org
>
> Committed: https://chromium.googlesource.com/external/webrtc/+/f14c47a58cb2a333cb9b11aef593f0e632fdb28a

TBR=tommi@webrtc.org,pbos@webrtc.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=

Review URL: https://codereview.webrtc.org/1736663004

Cr-Commit-Position: refs/heads/master@{#11761}
diff --git a/webrtc/modules/bitrate_controller/bitrate_controller_impl.cc b/webrtc/modules/bitrate_controller/bitrate_controller_impl.cc
index bf60878..72a5ff5 100644
--- a/webrtc/modules/bitrate_controller/bitrate_controller_impl.cc
+++ b/webrtc/modules/bitrate_controller/bitrate_controller_impl.cc
@@ -162,15 +162,16 @@
       kBitrateControllerUpdateIntervalMs - time_since_update_ms, 0);
 }
 
-void BitrateControllerImpl::Process() {
+int32_t BitrateControllerImpl::Process() {
   if (TimeUntilNextProcess() > 0)
-    return;
+    return 0;
   {
     rtc::CritScope cs(&critsect_);
     bandwidth_estimation_.UpdateEstimate(clock_->TimeInMilliseconds());
   }
   MaybeTriggerOnNetworkChanged();
   last_bitrate_update_ms_ = clock_->TimeInMilliseconds();
+  return 0;
 }
 
 void BitrateControllerImpl::OnReceivedRtcpReceiverReport(