Disable sending persistent histograms from last session by default.

chrome/browser/metrics/chrome_metrics_service_client.cc

Index: chrome/browser/metrics/chrome_metrics_service_client.cc
diff --git a/chrome/browser/metrics/chrome_metrics_service_client.cc b/chrome/browser/metrics/chrome_metrics_service_client.cc
index 65f7d09014d5c0db89b6b3eae299df31003815b8..703185bcbe25f694a3cba5f8618133499f0be9af 100644
--- a/chrome/browser/metrics/chrome_metrics_service_client.cc
+++ b/chrome/browser/metrics/chrome_metrics_service_client.cc
@@ -210,9 +210,15 @@ std::unique_ptr<metrics::FileMetricsProvider> CreateFileMetricsProvider(
 
   base::FilePath user_data_dir;
   if (base::PathService::Get(chrome::DIR_USER_DATA, &user_data_dir)) {
-    // Register the file holding browser metrics.
+    // Reporting of persistent histograms from last session is controlled by
+    // a feature param. TODO(bcwhite): The current default is not to upload
+    // until some issues are resolved. See crbug.com/706422 for details.
+    std::string send_unreported = variations::GetVariationParamValueByFeature(
+        base::kPersistentHistogramsFeature, "send_unreported_metrics");
+    boolean report_previous_persistent_histograms =

[bcwhite, 2017/03/29 16:09:12]

boolean => bool

[Alexei Svitkine (slow), 2017/03/29 16:19:01]

Oops, teaches for sending right before lunch before having a chance to compile.
Done.

+        metrics_reporting_enabled && (send_unreported == "yes");
     RegisterOrRemovePreviousRunMetricsFile(
-        metrics_reporting_enabled, user_data_dir,
+        report_previous_persistent_histograms, user_data_dir,
         ChromeMetricsServiceClient::kBrowserMetricsName, task_runner,
         file_metrics_provider.get());