Skip collection and upload of metrics if offline.

components/metrics/metrics_service.cc

Index: components/metrics/metrics_service.cc
diff --git a/components/metrics/metrics_service.cc b/components/metrics/metrics_service.cc
index 529af17d829491521866ac870048baf24d07d1a7..afe3dce214d10fe7fab5ceb2509158eadd516e1d 100644
--- a/components/metrics/metrics_service.cc
+++ b/components/metrics/metrics_service.cc
@@ -157,6 +157,7 @@
 #include "components/prefs/pref_registry_simple.h"
 #include "components/prefs/pref_service.h"
 #include "components/variations/entropy_provider.h"
+#include "net/base/network_change_notifier.h"

[Steven Holte, 2017/04/12 23:26:23]

I don't think net/ is allowed here, so this probably would need to be wrapped in
MetricsServiceClient or similar.

 
 namespace metrics {
 
@@ -727,6 +728,12 @@ void MetricsService::StartScheduledUpload() {
     return;
   }
 
+  // Don't try to send existing logs or to collecting something new if there is
+  // no network connection. A cumulative log will be created at the next (or
+  // future) upload time when a network connection is available.
+  if (net::NetworkChangeNotifier::IsOffline())

[Steven Holte, 2017/04/12 23:11:37]

You should call (or schedule a call to) rotation_scheduler_->RotationFinished()
before exiting this function.

Collection of logs while offline is already somewhat suppressed.  The next if
condition checks has_unsent_logs, and if so, avoids generating a log.  So this
change will suppress generation of at most one log.

[Steven Holte, 2017/04/12 23:26:23]

Actually after rereading the code, this will also suppress generation of
"initial" logs if we happen to be in Offline mode at startup (state !=
SENDING_LOGS), so we'd be generating one log per session instead of 2, which
seems more significant, though that also means that we could generate a large
"initial" log.

[bcwhite, 2017/04/18 14:56:44]

Sounds like it's not worth it, then.  One (or even two) pending logs should be
fine; it's if it grows without bound that could be a problem for devices that
are off-line for hours or even days at a time but still viewing offline content
during that interval.

+    return;
+
   // If there are unsent logs, send the next one. If not, start the asynchronous
   // process of finalizing the current log for upload.
   if (state_ == SENDING_LOGS && has_unsent_logs()) {