Adding Finch and flag for Sign-in promo

ios/chrome/browser/about_flags.mm

Index: ios/chrome/browser/about_flags.mm
diff --git a/ios/chrome/browser/about_flags.mm b/ios/chrome/browser/about_flags.mm
index b89a3bed98ad12e1a1355fb04961f5f91d16d54b..126063b299eb7937d0c5f0ec0ec78e7592a8d44e 100644
--- a/ios/chrome/browser/about_flags.mm
+++ b/ios/chrome/browser/about_flags.mm
@@ -27,6 +27,7 @@
 #include "components/flags_ui/flags_ui_switches.h"
 #include "components/ntp_tiles/switches.h"
 #include "components/reading_list/core/reading_list_switches.h"
+#include "components/signin/core/common/signin_switches.h"
 #include "components/strings/grit/components_strings.h"
 #include "ios/chrome/browser/chrome_switches.h"
 #include "ios/chrome/grit/ios_strings.h"
@@ -231,6 +232,14 @@ void AppendSwitchesFromExperimentalSettings(base::CommandLine* command_line) {
     command_line->AppendArguments(temp_command_line, false);
   }
 
+  // Populate command line flag for Suggestions UI display.
+  NSString* enableSigninPromo = [defaults stringForKey:@"EnableSigninPromo"];
+  if ([enableSigninPromo isEqualToString:@"Enabled"]) {
+    command_line->AppendSwitch(switches::kEnableSigninPromo);
+  } else if ([enableSigninPromo isEqualToString:@"Disabled"]) {
+    command_line->AppendSwitch(switches::kDisableSigninPromo);
+  }
+
   ios::GetChromeBrowserProvider()->AppendSwitchesFromExperimentalSettings(
       defaults, command_line);
 }