Revert of New method StatsObserver::OnCompleteReports, passing ownership. (patchset #2 id:20001 of https://codereview.webrtc.org/2584553002/ )

Reason for revert:
The new method doesn't work as intended.

It can't pass ownership, because the StatsReports is a vector of raw pointers to StatReport objects owned by the StatsCollector.

Original issue's description:
> New method StatsObserver::OnCompleteReports, passing ownership.
>
> The new name, OnCompleteReports rather than OnComplete, is needed
> because in C++ method lookup, overriding a method hides all otherwise
> inherited methods with the same name, even if they have a different
> signature. And here, the intention is that each subclass should
> override one or the other of the two methods, and inherit the method it
> doesn't override.
>
> This cl is a prerequisite for
> https://codereview.webrtc.org/2567143003/, because the Chrome glue
> code needs to retain the stats report after the OnComplete method has
> returned.
>
> Currently, Chrome makes a copy of the stats mapping (which breaks when
> changing ValuePtr from an rtc::linked_ptr to an std::unique_ptr). After
> this cl, Chrome can be fixed to take ownership and no longer needs to
> copy anything, unblocking cl 2567143003.
>
> BUG=webrtc:6424
>
> Review-Url: https://codereview.webrtc.org/2584553002
> Cr-Commit-Position: refs/heads/master@{#15708}
> Committed: b36ee8d498

TBR=solenberg@webrtc.org,magjed@webrtc.org,tkchin@webrtc.org,hbos@webrtc.org
# Not skipping CQ checks because original CL landed more than 1 days ago.
BUG=webrtc:6424

Review-Url: https://codereview.webrtc.org/2641783002
Cr-Commit-Position: refs/heads/master@{#16144}

webrtc/api/peerconnection.cc

@@ -1606,9 +1606,9 @@ void PeerConnection::OnMessage(rtc::Message* msg) {
     }
     case MSG_GETSTATS: {
       GetStatsMsg* param = static_cast<GetStatsMsg*>(msg->pdata);
-      std::unique_ptr<StatsReports> reports(new StatsReports);
+      StatsReports reports;
-      stats_->GetStats(param->track, reports.get());
+      stats_->GetStats(param->track, &reports);
-      param->observer->OnCompleteReports(std::move(reports));
+      param->observer->OnComplete(reports);
       delete param;
       break;
     }

webrtc/api/peerconnectioninterface.h

@@ -109,14 +109,7 @@ class StreamCollectionInterface : public rtc::RefCountInterface {
 
 class StatsObserver : public rtc::RefCountInterface {
  public:
-  // TODO(nisse, hbos): Old version, not passing ownership. Should
+  virtual void OnComplete(const StatsReports& reports) = 0;
-  // perhaps be deprecated, but since all of this is a legacy
-  // interface anyway, probably best to leave as is until this class
-  // can be deleted.
-  virtual void OnComplete(const StatsReports& reports) {}
-  virtual void OnCompleteReports(std::unique_ptr<StatsReports> reports) {
-    OnComplete(*reports);
-  }
 
  protected:
   virtual ~StatsObserver() {}

webrtc/api/test/mockpeerconnectionobservers.h

@@ -108,12 +108,12 @@ class MockStatsObserver : public webrtc::StatsObserver {
   MockStatsObserver() : called_(false), stats_() {}
   virtual ~MockStatsObserver() {}
 
-  void OnCompleteReports(std::unique_ptr<StatsReports> reports) override {
+  virtual void OnComplete(const StatsReports& reports) {
     ASSERT(!called_);
     called_ = true;
     stats_.Clear();
-    stats_.number_of_reports = reports->size();
+    stats_.number_of_reports = reports.size();
-    for (const auto* r : *reports) {
+    for (const auto* r : reports) {
       if (r->type() == StatsReport::kStatsReportTypeSsrc) {
         stats_.timestamp = r->timestamp();
         GetIntValue(r, StatsReport::kStatsValueNameAudioOutputLevel,

webrtc/sdk/android/src/jni/peerconnection_jni.cc

@@ -740,9 +740,9 @@ class StatsObserverWrapper : public StatsObserver {
 
   virtual ~StatsObserverWrapper() {}
 
-  void OnCompleteReports(std::unique_ptr<StatsReports> reports) override {
+  void OnComplete(const StatsReports& reports) override {
     ScopedLocalRefFrame local_ref_frame(jni());
-    jobjectArray j_reports = ReportsToJava(jni(), *reports);
+    jobjectArray j_reports = ReportsToJava(jni(), reports);
     jmethodID m = GetMethodID(jni(), *j_observer_class_, "onComplete",
                               "([Lorg/webrtc/StatsReport;)V");
     jni()->CallVoidMethod(*j_observer_global_, m, j_reports);

webrtc/sdk/objc/Framework/Classes/RTCPeerConnection+Stats.mm

@@ -29,10 +29,10 @@ class StatsObserverAdapter : public StatsObserver {
     completion_handler_ = nil;
   }
 
-  void OnCompleteReports(std::unique_ptr<StatsReports> reports) override {
+  void OnComplete(const StatsReports& reports) override {
     RTC_DCHECK(completion_handler_);
-    NSMutableArray *stats = [NSMutableArray arrayWithCapacity:reports->size()];
+    NSMutableArray *stats = [NSMutableArray arrayWithCapacity:reports.size()];
-    for (const auto* report : *reports) {
+    for (const auto* report : reports) {
       RTCLegacyStatsReport *statsReport =
           [[RTCLegacyStatsReport alloc] initWithNativeReport:*report];
       [stats addObject:statsReport];