Use “stop” not “cancel” buttons.

// FREEBIE

Signal/src/view controllers/AttachmentApprovalViewController.swift

@@ -38,7 +38,7 @@ class AttachmentApprovalViewController: UIViewController {
 
         view.backgroundColor = UIColor.black
 
-        self.navigationItem.leftBarButtonItem = UIBarButtonItem(barButtonSystemItem:.done,
+        self.navigationItem.leftBarButtonItem = UIBarButtonItem(barButtonSystemItem:.stop,
             target:self,
             action:#selector(donePressed))
         self.navigationItem.title = NSLocalizedString("ATTACHMENT_APPROVAL_DIALOG_TITLE",

Signal/src/view controllers/ContactsPicker.swift

@@ -91,11 +91,11 @@ open class ContactsPicker: UIViewController, UITableViewDelegate, UITableViewDat
     }
     
     func initializeBarButtons() {
-        let cancelButton = UIBarButtonItem(barButtonSystemItem: UIBarButtonSystemItem.cancel, target: self, action: #selector(onTouchCancelButton))
+        let cancelButton = UIBarButtonItem(barButtonSystemItem: .stop, target: self, action: #selector(onTouchCancelButton))
         self.navigationItem.leftBarButtonItem = cancelButton
         
         if multiSelectEnabled {
-            let doneButton = UIBarButtonItem(barButtonSystemItem: UIBarButtonSystemItem.done, target: self, action: #selector(onTouchDoneButton))
+            let doneButton = UIBarButtonItem(barButtonSystemItem: .done, target: self, action: #selector(onTouchDoneButton))
             self.navigationItem.rightBarButtonItem = doneButton
         }
     }