[iOS] Upstream experimental_flags::IsAlertOnBackgroundUploadEnabled

BUG=429756

Review URL: https://codereview.chromium.org/1131303003

Cr-Commit-Position: refs/heads/master@{#329628}

ios/chrome/browser/experimental_flags.h

@@ -12,6 +12,9 @@
 
 namespace experimental_flags {
 
+// Whether background crash report upload should generate a local notification.
+bool IsAlertOnBackgroundUploadEnabled();
+
 // Returns true if the contents of the clipboard can be used for autocomplete.
 bool IsOpenFromClipboardEnabled();
 

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);