Avoid some pref writes in MetricsLog. Ensure some stability metrics are cleared.

components/metrics/metrics_log.cc

Index: components/metrics/metrics_log.cc
diff --git a/components/metrics/metrics_log.cc b/components/metrics/metrics_log.cc
index 3d8cc1886a891d566bc3e42237c97ff41b385618..691a946f9e6796d0ecd7051eddcbf569d51cc4d6 100644
--- a/components/metrics/metrics_log.cc
+++ b/components/metrics/metrics_log.cc
@@ -203,37 +203,45 @@ void MetricsLog::RecordStabilityMetrics(
     metrics_providers[i]->ProvideStabilityMetrics(system_profile);
   }
 
-  // Omit some stats unless this is the initial stability log.
-  if (log_type() != INITIAL_STABILITY_LOG)
-    return;
+  SystemProfileProto::Stability* stability =
+      system_profile->mutable_stability();
 
   int incomplete_shutdown_count =
       pref->GetInteger(prefs::kStabilityIncompleteSessionEndCount);
-  pref->SetInteger(prefs::kStabilityIncompleteSessionEndCount, 0);
+  if (incomplete_shutdown_count) {
+    pref->SetInteger(prefs::kStabilityIncompleteSessionEndCount, 0);
+    stability->set_incomplete_shutdown_count(incomplete_shutdown_count);
+  }
+
   int breakpad_registration_success_count =
       pref->GetInteger(prefs::kStabilityBreakpadRegistrationSuccess);
-  pref->SetInteger(prefs::kStabilityBreakpadRegistrationSuccess, 0);
+  if (breakpad_registration_success_count) {
+    pref->SetInteger(prefs::kStabilityBreakpadRegistrationSuccess, 0);
+    stability->set_breakpad_registration_success_count(
+        breakpad_registration_success_count);
+  }
+
   int breakpad_registration_failure_count =
       pref->GetInteger(prefs::kStabilityBreakpadRegistrationFail);
-  pref->SetInteger(prefs::kStabilityBreakpadRegistrationFail, 0);
+  if (breakpad_registration_failure_count) {
+    pref->SetInteger(prefs::kStabilityBreakpadRegistrationFail, 0);
+    stability->set_breakpad_registration_failure_count(
+        breakpad_registration_failure_count);
+  }
+
   int debugger_present_count =
       pref->GetInteger(prefs::kStabilityDebuggerPresent);
-  pref->SetInteger(prefs::kStabilityDebuggerPresent, 0);
+  if (debugger_present_count) {
+    pref->SetInteger(prefs::kStabilityDebuggerPresent, 0);
+    stability->set_debugger_present_count(debugger_present_count);
+  }
+
   int debugger_not_present_count =
       pref->GetInteger(prefs::kStabilityDebuggerNotPresent);
-  pref->SetInteger(prefs::kStabilityDebuggerNotPresent, 0);
-
-  // TODO(jar): The following are all optional, so we *could* optimize them for
-  // values of zero (and not include them).
-  SystemProfileProto::Stability* stability =
-      system_profile->mutable_stability();
-  stability->set_incomplete_shutdown_count(incomplete_shutdown_count);
-  stability->set_breakpad_registration_success_count(
-      breakpad_registration_success_count);
-  stability->set_breakpad_registration_failure_count(
-      breakpad_registration_failure_count);
-  stability->set_debugger_present_count(debugger_present_count);
-  stability->set_debugger_not_present_count(debugger_not_present_count);
+  if (debugger_not_present_count) {
+    pref->SetInteger(prefs::kStabilityDebuggerNotPresent, 0);
+    stability->set_debugger_not_present_count(debugger_not_present_count);
+  }
 }
 
 void MetricsLog::RecordGeneralMetrics(
@@ -285,9 +293,11 @@ bool MetricsLog::HasStabilityMetrics() const {
 // protobufs is complete.
 void MetricsLog::WriteRequiredStabilityAttributes(PrefService* pref) {
   int launch_count = pref->GetInteger(prefs::kStabilityLaunchCount);
-  pref->SetInteger(prefs::kStabilityLaunchCount, 0);
+  if (launch_count)
+    pref->SetInteger(prefs::kStabilityLaunchCount, 0);
   int crash_count = pref->GetInteger(prefs::kStabilityCrashCount);
-  pref->SetInteger(prefs::kStabilityCrashCount, 0);
+  if (crash_count)
+    pref->SetInteger(prefs::kStabilityCrashCount, 0);
 
   SystemProfileProto::Stability* stability =
       uma_proto()->mutable_system_profile()->mutable_stability();
@@ -379,15 +389,15 @@ void MetricsLog::RecordEnvironment(
   for (size_t i = 0; i < metrics_providers.size(); ++i)
     metrics_providers[i]->ProvideSystemProfileMetrics(system_profile);
 
-  std::string serialied_system_profile;
+  std::string serialized_system_profile;
   std::string base64_system_profile;
-  if (system_profile->SerializeToString(&serialied_system_profile)) {
-    base::Base64Encode(serialied_system_profile, &base64_system_profile);
+  if (system_profile->SerializeToString(&serialized_system_profile)) {
+    base::Base64Encode(serialized_system_profile, &base64_system_profile);
     PrefService* local_state = local_state_;
     local_state->SetString(prefs::kStabilitySavedSystemProfile,
                            base64_system_profile);
     local_state->SetString(prefs::kStabilitySavedSystemProfileHash,
-                           ComputeSHA1(serialied_system_profile));
+                           ComputeSHA1(serialized_system_profile));
   }
 }
 
@@ -404,10 +414,11 @@ bool MetricsLog::LoadSavedEnvironmentFromPrefs() {
   local_state->ClearPref(prefs::kStabilitySavedSystemProfileHash);
 
   SystemProfileProto* system_profile = uma_proto()->mutable_system_profile();
-  std::string serialied_system_profile;
-  return base::Base64Decode(base64_system_profile, &serialied_system_profile) &&
-         ComputeSHA1(serialied_system_profile) == system_profile_hash &&
-         system_profile->ParseFromString(serialied_system_profile);
+  std::string serialized_system_profile;
+  return base::Base64Decode(base64_system_profile,
+                            &serialized_system_profile) &&
+         ComputeSHA1(serialized_system_profile) == system_profile_hash &&
+         system_profile->ParseFromString(serialized_system_profile);
 }
 
 void MetricsLog::CloseLog() {