Adding reporting of metrics sampling rate.

chrome/browser/metrics/chrome_metrics_services_manager_client.cc

Index: chrome/browser/metrics/chrome_metrics_services_manager_client.cc
diff --git a/chrome/browser/metrics/chrome_metrics_services_manager_client.cc b/chrome/browser/metrics/chrome_metrics_services_manager_client.cc
index a31d9af6a10d4291b9d515ff2d0631a7f3f1fe11..61dc5dc149381f24714d61314b99f68d7c228a3d 100644
--- a/chrome/browser/metrics/chrome_metrics_services_manager_client.cc
+++ b/chrome/browser/metrics/chrome_metrics_services_manager_client.cc
@@ -8,6 +8,7 @@
 #include "base/feature_list.h"
 #include "base/logging.h"
 #include "base/memory/ptr_util.h"
+#include "base/strings/string_number_conversions.h"
 #include "chrome/browser/browser_process.h"
 #include "chrome/browser/metrics/chrome_metrics_service_accessor.h"
 #include "chrome/browser/metrics/chrome_metrics_service_client.h"
@@ -21,10 +22,20 @@
 #include "components/prefs/pref_service.h"
 #include "components/rappor/rappor_service.h"
 #include "components/variations/service/variations_service.h"
+#include "components/variations/variations_associated_data.h"
 #include "content/public/browser/browser_thread.h"
 
 namespace {
 
+// Name of the variations param that defines the sampling rate.
+const char kRateParamName[] = "sampling_rate_per_mille";
+
+// Metrics reporting feature. This feature, along with user consent, controls if
+// recording and reporting are enabled. If the feature is enabled, but no
+// consent is given, then there will be no recording or reporting.
+const base::Feature kMetricsReportingFeature{"MetricsReporting",
+                                             base::FEATURE_ENABLED_BY_DEFAULT};
+
 // Posts |GoogleUpdateSettings::StoreMetricsClientInfo| on blocking pool thread
 // because it needs access to IO and cannot work from UI thread.
 void PostStoreMetricsClientInfo(const metrics::ClientInfo& client_info) {
@@ -33,10 +44,16 @@ void PostStoreMetricsClientInfo(const metrics::ClientInfo& client_info) {
       base::Bind(&GoogleUpdateSettings::StoreMetricsClientInfo, client_info));
 }
 
+// Only clients that were given an opt-out metrics-reporting consent flow are
+// eligible for sampling.
+bool IsClientEligibleForSampling() {
+  return metrics::GetMetricsReportingDefaultState(
+             g_browser_process->local_state()) ==
+         metrics::EnableMetricsDefault::OPT_OUT;
+}
+
 }  // namespace
 
-const base::Feature kMetricsReportingFeature{"MetricsReporting",
-                                             base::FEATURE_ENABLED_BY_DEFAULT};
 
 class ChromeMetricsServicesManagerClient::ChromeEnabledStateProvider
     : public metrics::EnabledStateProvider {
@@ -50,7 +67,7 @@ class ChromeMetricsServicesManagerClient::ChromeEnabledStateProvider
 
   bool IsReportingEnabled() override {
     return IsConsentGiven() &&
-           base::FeatureList::IsEnabled(kMetricsReportingFeature);
+        ChromeMetricsServicesManagerClient::IsClientInSample();
   }
 
   DISALLOW_COPY_AND_ASSIGN(ChromeEnabledStateProvider);
@@ -67,6 +84,45 @@ ChromeMetricsServicesManagerClient::ChromeMetricsServicesManagerClient(
 
 ChromeMetricsServicesManagerClient::~ChromeMetricsServicesManagerClient() {}
 
+// static
+bool ChromeMetricsServicesManagerClient::IsClientInSample() {
+  // Only some clients are eligible for sampling. Clients that aren't eligible
+  // will always be considered "in sample". In this case, we don't want the
+  // feature state queried, because we don't want the field trial that controls
+  // sampling to be reported as active.
+  if (!IsClientEligibleForSampling()) {

[Alexei Svitkine (slow), 2016/08/01 15:49:56]

Nit: No {}'s


Same below for 1-liners.

[jwd, 2016/08/01 16:45:29]

Done.

+    return true;
+  }
+
+  return base::FeatureList::IsEnabled(kMetricsReportingFeature);
+}
+
+// static
+int ChromeMetricsServicesManagerClient::GetSamplingRatePerMille() {
+  // The population that is NOT eligible for sampling in considered "in sample",
+  // so that population's sampling rate is 1000/1000.
+  if (!IsClientEligibleForSampling()) {
+    return 1000;
+  }
+
+  std::string rate_str = variations::GetVariationParamValueByFeature(
+      kMetricsReportingFeature, kRateParamName);
+  if (rate_str.empty()) {
+    // The parameter can be empty either if the feature is dissabled, or the

[Alexei Svitkine (slow), 2016/08/01 15:49:56]

disabled - also mispeled below

[jwd, 2016/08/01 16:45:29]

Done.

+    // parameter isn't defined in an associated variation. The dissabled case is
+    // unimportant, since no metrics are reported. If the parameter is
+    // undefined, assume sampling is not being done, i.e. the sample rate is
+    // 1000/1000.
+    return 1000;
+  }
+
+  int rate;
+  if (!base::StringToInt(rate_str, &rate) || rate > 1000) {
+    return 1000;
+  }
+  return rate;
+}
+
 std::unique_ptr<rappor::RapporService>
 ChromeMetricsServicesManagerClient::CreateRapporService() {
   DCHECK(thread_checker_.CalledOnValidThread());