[iOS] Upstream experimental_flags::IsAlertOnBackgroundUploadEnabled

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 f837e62ddf8a83b7af54f59c1eb09aa3731c7f1f..6adfb739566cd02c8f21b3061d8d0347c97eb8c2 100644
--- a/ios/chrome/browser/experimental_flags.mm
+++ b/ios/chrome/browser/experimental_flags.mm
@@ -15,8 +15,18 @@
 #include "components/variations/variations_associated_data.h"
 #include "ios/chrome/browser/chrome_switches.h"
 
+namespace {
+NSString* const kEnableAlertOnBackgroundUpload =
+    @"EnableAlertsOnBackgroundUpload";
+}  // namespace
+
 namespace experimental_flags {
 
+bool IsAlertOnBackgroundUploadEnabled() {
+  return [[NSUserDefaults standardUserDefaults]
+      boolForKey:kEnableAlertOnBackgroundUpload];
+}
+
 bool IsOpenFromClipboardEnabled() {
   base::CommandLine* command_line = base::CommandLine::ForCurrentProcess();
   return command_line->HasSwitch(switches::kEnableIOSOpenFromClipboard);