Log base::Features in Launch.FlagsAtStartup

chrome/browser/about_flags.cc

Index: chrome/browser/about_flags.cc
diff --git a/chrome/browser/about_flags.cc b/chrome/browser/about_flags.cc
index b57dcedf7dc67ef5c5958274de5fb298a267abac..82969f35f281dfd56e29b96506a72b3af128f3f7 100644
--- a/chrome/browser/about_flags.cc
+++ b/chrome/browser/about_flags.cc
@@ -2227,7 +2227,9 @@ void ResetAllFlags(flags_ui::FlagsStorage* flags_storage) {
 void RecordUMAStatistics(flags_ui::FlagsStorage* flags_storage) {
   const std::set<std::string> switches =
       FlagsStateSingleton::GetFlagsState()->GetSwitchesFromFlags(flags_storage);
-  ReportAboutFlagsHistogram("Launch.FlagsAtStartup", switches);
+  const std::set<std::string> features =
+      FlagsStateSingleton::GetFlagsState()->GetFeaturesFromFlags(flags_storage);
+  ReportAboutFlagsHistogram("Launch.FlagsAtStartup", switches, features);
 }
 
 base::HistogramBase::Sample GetSwitchUMAId(const std::string& switch_name) {
@@ -2235,9 +2237,17 @@ base::HistogramBase::Sample GetSwitchUMAId(const std::string& switch_name) {
       base::HashMetricName(switch_name));
 }
 
-void ReportAboutFlagsHistogram(const std::string& uma_histogram_name,
-                               const std::set<std::string>& flags) {
-  for (const std::string& flag : flags) {
+void ReportAboutFlagsHistogram(
+    const std::string& uma_histogram_name,
+    const std::set<std::string>& switches,
+    const std::set<std::string>& features) {
+  ReportAboutFlagsHistogramSwitches(uma_histogram_name, switches);
+  ReportAboutFlagsHistogramFeatures(uma_histogram_name, features);
+}
+
+void ReportAboutFlagsHistogramSwitches(const std::string& uma_histogram_name,
+                                       const std::set<std::string>& switches) {
+  for (const std::string& flag : switches) {
     int uma_id = about_flags::testing::kBadSwitchFormatHistogramId;
     if (base::StartsWith(flag, "--", base::CompareCase::SENSITIVE)) {
       // Skip '--' before switch name.
@@ -2262,6 +2272,21 @@ void ReportAboutFlagsHistogram(const std::string& uma_histogram_name,
   }
 }
 
+void ReportAboutFlagsHistogramFeatures(const std::string& uma_histogram_name,

[Alexei Svitkine (slow), 2016/09/16 15:52:38]

If this is not called from anywhere except this file, please move it into the
anonymous namespace at the top of the file. Also, please add a function comment
above it.

Same for the other function.

[lawrencewu, 2016/09/16 17:12:57]

Done.

+                                       const std::set<std::string>&features) {
+  for (const std::string& feature : features) {
+    int uma_id = about_flags::testing::kBadSwitchFormatHistogramId;
+
+    uma_id = GetSwitchUMAId(feature);
+    DVLOG(1) << "ReportAboutFlagsHistogram(): histogram='" << uma_histogram_name
+             << "' '" << feature << "', uma_id=" << uma_id;
+
+    // Sparse histogram macro does not cache the histogram, so it's safe
+    // to use macro with non-static histogram name here.
+    UMA_HISTOGRAM_SPARSE_SLOWLY(uma_histogram_name, uma_id);
+  }
+}
+
 namespace testing {
 
 const base::HistogramBase::Sample kBadSwitchFormatHistogramId = 0;