Adding Finch and flag for Sign-in promo

ios/chrome/browser/experimental_flags.mm

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // This file can be empty. Its purpose is to contain the relatively short lived
 // definitions required for experimental flags.
 
 #include "ios/chrome/browser/experimental_flags.h"
 
 #include <dispatch/dispatch.h>
 #import <Foundation/Foundation.h>
 
 #include <string>
 
 #include "base/command_line.h"
 #include "base/metrics/field_trial.h"
 #include "base/strings/string_util.h"
 #include "base/strings/sys_string_conversions.h"
 #include "components/autofill/core/common/autofill_switches.h"
+#include "components/signin/core/common/signin_switches.h"
 #include "components/variations/variations_associated_data.h"
 #include "ios/chrome/browser/chrome_switches.h"
 #include "ios/web/public/web_view_creation_util.h"
 
 #if !defined(__has_feature) || !__has_feature(objc_arc)
 #error "This file requires ARC support."
 #endif
 
 namespace {
 
@@ skipping 226 matching lines @@
   if (command_line->HasSwitch(switches::kEnableSuggestionsUI))
     return true;
 
   if (command_line->HasSwitch(switches::kDisableSuggestionsUI))
     return false;
 
   // By default, disable it.
   return false;
 }
 
+bool IsSigninPromoEnabled() {
+  // Check if the experimental flag is forced on or off.
+  base::CommandLine* command_line = base::CommandLine::ForCurrentProcess();
+  if (command_line->HasSwitch(switches::kEnableSigninPromo))
+    return true;
+  if (command_line->HasSwitch(switches::kDisableSigninPromo))
+    return false;
+  std::string group_name = base::FieldTrialList::FindFullName("IOSSigninPromo");
+  return base::StartsWith(group_name, "Enabled",
+                          base::CompareCase::INSENSITIVE_ASCII);
+}
+
 }  // namespace experimental_flags