Add perf histogram and tests for inline signin

chrome/browser/signin/signin_promo.cc

Index: chrome/browser/signin/signin_promo.cc
diff --git a/chrome/browser/signin/signin_promo.cc b/chrome/browser/signin/signin_promo.cc
index e2ac8ab5162ad04cbfd2c50bb5e588945bf21309..de67ec7d2e7015a94aa33a49ef43071e78f1df2b 100644
--- a/chrome/browser/signin/signin_promo.cc
+++ b/chrome/browser/signin/signin_promo.cc
@@ -4,6 +4,7 @@
 
 #include "chrome/browser/signin/signin_promo.h"
 
+#include "base/command_line.h"
 #include "base/prefs/pref_service.h"
 #include "base/strings/string_number_conversions.h"
 #include "base/strings/string_util.h"
@@ -21,6 +22,7 @@
 #include "chrome/browser/sync/profile_sync_service_factory.h"
 #include "chrome/browser/ui/webui/options/core_options_handler.h"
 #include "chrome/browser/ui/webui/theme_source.h"
+#include "chrome/common/chrome_switches.h"
 #include "chrome/common/net/url_util.h"
 #include "chrome/common/pref_names.h"
 #include "chrome/common/profile_management_switches.h"
@@ -118,6 +120,10 @@ bool ShouldShowPromoAtStartup(Profile* profile, bool is_new_profile) {
   if (profile->IsOffTheRecord())
     return false;
 
+  const CommandLine* command_line = CommandLine::ForCurrentProcess();
+  if (command_line->HasSwitch(switches::kForceSigninPromo))
+    return true;
+
   if (!ShouldShowPromo(profile))
     return false;