Send metrics with embedded system profiles after system startup.

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..b6d615f3e86191a6b6b31b71a6e9f3a626ed953a 100644
--- a/components/metrics/metrics_service.cc
+++ b/components/metrics/metrics_service.cc
@@ -783,9 +783,17 @@ bool MetricsService::PrepareInitialStabilityLog(
   // Do not call NotifyOnDidCreateMetricsLog here because the stability
   // log describes stats from the _previous_ session.
   std::string system_profile_app_version;
-  if (!initial_stability_log->LoadSavedEnvironmentFromPrefs(
-          &system_profile_app_version)) {
-    return false;
+  for (auto& provider : metrics_providers_) {
+    if (initial_stability_log->LoadSavedEnvironmentFromProvider(
+            provider.get(), &system_profile_app_version)) {

[Alexei Svitkine (slow), 2017/05/31 20:31:24]

Instead of replacing the profile of the stability log, can we generate a
separate log from each persistent file that has a system profile?

Otherwise if we have a scenario of:
  1. Session A crash
  2. Session B crash
  3. Session C OK

With your current CL, we will group stability stats + metrics from A and B with
one of the profiles of A or B - but that will not be correct for some of the
metrics in that report.

Instead, we should have:
  persistent histogram from A reported separately with its embedded profile
  persistent histogram from B reported separately with its embedded profile
  stability log just containing the non-persistent stuff with the system profile
from local state

[bcwhite, 2017/05/31 20:48:29]

Currently there is only ever one persistent histogram file and it's always for
the previous run so this scenario doesn't occur.  There are also other metrics
files (like from Startup and Crashpad) that don't have an embedded profile so
they can't be reported independently.

But generally I agree with you.  I'd like to get the system profile into every
persistent file and then move the reporting completely out to a separate task
that can be run sometime after startup or even by an outside process such as
Omaha.

Is this acceptable as a step along that path?

[Alexei Svitkine (slow), 2017/06/01 15:00:29]

Per offline discussion, I prefer to not have this intermediate step - as this
may report the stability metrics with the persistent histogram's system proto -
which can also be wrong. Let's just do the final solution.

+      break;
+    }
+  }
+  if (system_profile_app_version.empty()) {
+    if (!initial_stability_log->LoadSavedEnvironmentFromPrefs(
+            &system_profile_app_version)) {
+      return false;
+    }
   }
   if (system_profile_app_version != prefs_previous_version)
     StabilityMetricsProvider(local_state_).LogStabilityVersionMismatch();