Adding synthetic field trial for DataReductionProxyEnabled

chrome/browser/metrics/chrome_metrics_service_accessor.cc

Index: chrome/browser/metrics/chrome_metrics_service_accessor.cc
diff --git a/chrome/browser/metrics/chrome_metrics_service_accessor.cc b/chrome/browser/metrics/chrome_metrics_service_accessor.cc
index 6c142fc463278d90a643c84e5a9e44518e4c68b6..3ef130ff299fd9a3d4e3d90324c4cd926f8fbe3f 100644
--- a/chrome/browser/metrics/chrome_metrics_service_accessor.cc
+++ b/chrome/browser/metrics/chrome_metrics_service_accessor.cc
@@ -8,6 +8,7 @@
 #include "chrome/browser/browser_process.h"
 #include "chrome/common/pref_names.h"
 #include "components/metrics/metrics_service.h"
+#include "components/variations/metrics_util.h"
 
 #if defined(OS_CHROMEOS)
 #include "chrome/browser/chromeos/settings/cros_settings.h"
@@ -46,3 +47,14 @@ bool ChromeMetricsServiceAccessor::IsCrashReportingEnabled() {
   return false;
 #endif
 }
+
+// static
+void ChromeMetricsServiceAccessor::RegisterSyntheticFieldTrial(
+    std::string trial, std::string group) {
+  if (g_browser_process->metrics_service()) {

[bengr, 2014/07/30 19:08:22]

Would we ever not have a metrics_service? It would be nice if the caller could
know that registration was a no-op.

[megjablon, 2014/07/30 21:27:07]

g_browser_process->metrics_service() may return null

we can return false if the service is not available so the registration didn't
happen

+    SyntheticTrialGroup trial_group(metrics::HashName(trial),
+                                    metrics::HashName(group));
+    g_browser_process->metrics_service()->RegisterSyntheticFieldTrial(
+        trial_group);
+  }
+}