Enable Update Password UI on iOS behind a flag

ios/chrome/browser/experimental_flags.mm

Index: ios/chrome/browser/experimental_flags.mm
diff --git a/ios/chrome/browser/experimental_flags.mm b/ios/chrome/browser/experimental_flags.mm
index 5e6be562c46df578d8abf208c01bef8ee9a0e692..9e772354a4ad3e36c15db17bfaee08e53242ea9f 100644
--- a/ios/chrome/browser/experimental_flags.mm
+++ b/ios/chrome/browser/experimental_flags.mm
@@ -27,6 +27,7 @@ NSString* const kEnableViewCopyPasswords = @"EnableViewCopyPasswords";
 NSString* const kHeuristicsForPasswordGeneration =
     @"HeuristicsForPasswordGeneration";
 NSString* const kEnableReadingList = @"EnableReadingList";
+NSString* const kUpdatePasswordUIEnabled = @"UpdatePasswordUIEnabled";
 }  // namespace
 
 namespace experimental_flags {
@@ -136,4 +137,9 @@ bool IsPhysicalWebEnabled() {
                           base::CompareCase::INSENSITIVE_ASCII);
 }
 
+bool IsUpdatePasswordUIEnabled() {
+  return [[NSUserDefaults standardUserDefaults]
+      boolForKey:kUpdatePasswordUIEnabled];
+}
+
 }  // namespace experimental_flags