[ObjC ARC] Converts ios/chrome/browser/passwords:passwords to ARC.

ios/chrome/browser/passwords/js_password_manager.mm

Index: ios/chrome/browser/passwords/js_password_manager.mm
diff --git a/ios/chrome/browser/passwords/js_password_manager.mm b/ios/chrome/browser/passwords/js_password_manager.mm
index 15d879c90668aec7dc2a0042b3e8b65571c3be9e..e28e8fc146ce673ac9c5f6d757f2201b2ed2bfa8 100644
--- a/ios/chrome/browser/passwords/js_password_manager.mm
+++ b/ios/chrome/browser/passwords/js_password_manager.mm
@@ -9,6 +9,10 @@
 #include "base/mac/foundation_util.h"
 #include "base/strings/sys_string_conversions.h"
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 namespace {
 // Sanitizes |JSONString| and wraps it in quotes so it can be injected safely in
 // JavaScript.