Flush UKM metrics when backgrounded on Android and iOS.

components/ukm/ukm_service.cc

 // Copyright 2017 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.
 
 #include "components/ukm/ukm_service.h"
 
 #include <memory>
 #include <string>
 #include <utility>
 
@@ skipping 180 matching lines @@
   DCHECK(thread_checker_.CalledOnValidThread());
   DVLOG(1) << "UkmService::DisableReporting";
 
   for (auto& provider : metrics_providers_)
     provider->OnRecordingDisabled();
 
   scheduler_->Stop();
   Flush();
 }
 
+#if defined(OS_ANDROID) || defined(OS_IOS)
+void UkmService::OnAppEnterForeground() {
+  DCHECK(thread_checker_.CalledOnValidThread());
+  DVLOG(1) << "UkmService::OnAppEnterForeground";
+
+  // If initialize_started_ is false, UKM has not yet been started, so bail.

[Alexei Svitkine (slow), 2017/03/01 23:24:02]

Nit: Mention that the scheduler will instead be started via EnableReporting().

[Bryan McQuade, 2017/03/01 23:37:10]

sure, done, thanks!

+  if (!initialize_started_)
+    return;
+
+  scheduler_->Start();
+}
+
+void UkmService::OnAppEnterBackground() {
+  DCHECK(thread_checker_.CalledOnValidThread());
+  DVLOG(1) << "UkmService::OnAppEnterBackground";
+
+  if (!initialize_started_)
+    return;
+
+  scheduler_->Stop();
+
+  // Give providers a chance to persist ukm data as part of being backgrounded.
+  for (auto& provider : metrics_providers_)
+    provider->OnAppEnterBackground();
+
+  Flush();
+}
+#endif
+
 void UkmService::Flush() {
   DCHECK(thread_checker_.CalledOnValidThread());
   if (initialize_complete_)
     BuildAndStoreLog();
   persisted_logs_.PersistUnsentLogs();
 }
 
 void UkmService::Purge() {
   DCHECK(thread_checker_.CalledOnValidThread());
   DVLOG(1) << "UkmService::Purge";
@@ skipping 199 matching lines @@
   }
   if (entries_.size() >= kMaxEntries) {
     RecordDroppedEntry(DroppedDataReason::MAX_HIT);
     return;
   }
 
   entries_.push_back(std::move(entry));
 }
 
 }  // namespace ukm