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: f14c47a58c

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}

webrtc/modules/rtp_rtcp/include/receive_statistics.h

@@ -90,7 +90,7 @@ class NullReceiveStatistics : public ReceiveStatistics {
   StatisticianMap GetActiveStatisticians() const override;
   StreamStatistician* GetStatistician(uint32_t ssrc) const override;
   int64_t TimeUntilNextProcess() override;
-  void Process() override;
+  int32_t Process() override;
   void SetMaxReorderingThreshold(int max_reordering_threshold) override;
   void RegisterRtcpStatisticsCallback(
       RtcpStatisticsCallback* callback) override;