Add an override flag to enable metrics reporting.

chrome/common/chrome_switches.cc

Index: chrome/common/chrome_switches.cc
diff --git a/chrome/common/chrome_switches.cc b/chrome/common/chrome_switches.cc
index dae4ac615576da77149cbdf6acd5b8ed9c208746..a7a89ef110fcc4cfb195002e266977ce98569062 100644
--- a/chrome/common/chrome_switches.cc
+++ b/chrome/common/chrome_switches.cc
@@ -484,6 +484,9 @@ const char kForceDesktopIOSPromotion[] = "force-desktop-ios-promotion";
 // connection type.
 const char kForceEffectiveConnectionType[] = "force-effective-connection-type";
 
+// Forces metrics reporting to be enabled.
+const char kForceEnableMetricsReporting[] = "force-enable-metrics-reporting";
+
 // Displays the First Run experience when the browser is started, regardless of
 // whether or not it's actually the First Run (this overrides kNoFirstRun).
 const char kForceFirstRun[]                 = "force-first-run";