Remove MetricsServiceObserver in favor of MetricsProvider.

components/metrics/metrics_service.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 //------------------------------------------------------------------------------
 // Description of the life cycle of a instance of MetricsService.
 //
 //  OVERVIEW
 //
 // A MetricsService instance is typically created at application startup.  It is
@@ skipping 648 matching lines @@
 
   const int64 incremental_time_secs = incremental_uptime->InSeconds();
   if (incremental_time_secs > 0) {
     int64 metrics_uptime =
         pref->GetInt64(metrics::prefs::kUninstallMetricsUptimeSec);
     metrics_uptime += incremental_time_secs;
     pref->SetInt64(metrics::prefs::kUninstallMetricsUptimeSec, metrics_uptime);
   }
 }
 
-void MetricsService::AddObserver(MetricsServiceObserver* observer) {
-  DCHECK(thread_checker_.CalledOnValidThread());
-  observers_.AddObserver(observer);
-}
-
-void MetricsService::RemoveObserver(MetricsServiceObserver* observer) {
-  DCHECK(thread_checker_.CalledOnValidThread());
-  observers_.RemoveObserver(observer);
-}
-
 void MetricsService::NotifyOnDidCreateMetricsLog() {
-  DCHECK(thread_checker_.CalledOnValidThread());
-  FOR_EACH_OBSERVER(
-      MetricsServiceObserver, observers_, OnDidCreateMetricsLog());
+  DCHECK(IsSingleThreaded());

[Ilya Sherman, 2014/09/03 00:28:40]

nit: Hmm, is this change needed for this CL?  I've forgotten why we have both
IsSingleThreaded() and the thread_checker_ -- can you remind me?

[Alexei Svitkine (slow), 2014/09/03 13:24:41]

These were the only things using |thread_checker_|, so with this change only
this method was left, so I just removed it entirely.

I don't think both are necessary and I think we can probably move
IsSingleThreaded to use a ThreadChecker, but if we do that, we should change all
the code at once - which should be a separate CL.

   for (size_t i = 0; i < metrics_providers_.size(); ++i)
     metrics_providers_[i]->OnDidCreateMetricsLog();
 }
 
 //------------------------------------------------------------------------------
 // State save methods
 
 void MetricsService::ScheduleNextStateSave() {
   state_saver_factory_.InvalidateWeakPtrs();
 
@@ skipping 493 matching lines @@
   local_state_->SetBoolean(path, value);
   RecordCurrentState(local_state_);
 }
 
 void MetricsService::RecordCurrentState(PrefService* pref) {
   pref->SetInt64(metrics::prefs::kStabilityLastTimestampSec,
                  base::Time::Now().ToTimeT());
 }
 
 }  // namespace metrics