Add support for the ExperimentalSwReporterEngine field trial.

chrome/browser/safe_browsing/srt_field_trial_win.cc

Index: chrome/browser/safe_browsing/srt_field_trial_win.cc
diff --git a/chrome/browser/safe_browsing/srt_field_trial_win.cc b/chrome/browser/safe_browsing/srt_field_trial_win.cc
index 249b274d3071dbd8622775728328a89dd3e494da..31015b6168c40e8c67e254a44e0d18c3adc631a8 100644
--- a/chrome/browser/safe_browsing/srt_field_trial_win.cc
+++ b/chrome/browser/safe_browsing/srt_field_trial_win.cc
@@ -4,9 +4,12 @@
 
 #include "chrome/browser/safe_browsing/srt_field_trial_win.h"
 
+#include <sstream>

[grt (UTC plus 2), 2016/08/10 06:47:02]

unused?

[Joe Mason, 2016/08/15 17:24:40]

Done.

+
 #include "base/metrics/field_trial.h"
 #include "base/metrics/histogram.h"
 #include "base/strings/string_util.h"
+#include "base/strings/stringprintf.h"
 #include "components/variations/variations_associated_data.h"
 
 namespace {
@@ -23,6 +26,8 @@ const char kSRTElevationAsNeededGroup[] = "AsNeeded";
 const char kSRTReporterTrial[] = "srt_reporter";
 const char kSRTReporterOffGroup[] = "Off";
 
+const char kSRTStepMetricName[] = "SoftwareReporter.Step";
+
 // The download links of the Software Removal Tool.
 const char kMainSRTDownloadURL[] =
     "https://dl.google.com/dl"
@@ -70,8 +75,15 @@ void RecordSRTPromptHistogram(SRTPromptHistogramValue value) {
                             SRT_PROMPT_MAX);
 }
 
-void RecordReporterStepHistogram(SwReporterUmaValue value) {
-  UMA_HISTOGRAM_ENUMERATION("SoftwareReporter.Step", value, SW_REPORTER_MAX);
+void RecordReporterStepHistogram(SwReporterUmaValue value,
+                                 const std::string& suffix) {
+  if (suffix.empty()) {
+    UMA_HISTOGRAM_ENUMERATION(kSRTStepMetricName, value, SW_REPORTER_MAX);
+    return;
+  }
+  UMA_HISTOGRAM_ENUMERATION(
+      base::StringPrintf("%s_%s", kSRTStepMetricName, suffix).c_str(),

[grt (UTC plus 2), 2016/08/10 06:47:02]

due to the way the histogram macros work, you can't compute the histogram name
in the macro invocation. you'll have to call base::LinearHistogram::FactoryGet
and Add yourself.

[Joe Mason, 2016/08/15 17:24:40]

Done. (Relies on the refactor to add UMAHistogramReporter in
http://crrev.com/2243303002)

+      value, SW_REPORTER_MAX);
 }
 
 }  // namespace safe_browsing