Creates alertCoordinatorDelegate for alerts

ios/chrome/browser/ui/alert_coordinator/modal_alert.mm

Index: ios/chrome/browser/ui/alert_coordinator/modal_alert.mm
diff --git a/ios/chrome/browser/ui/alert_coordinator/modal_alert.mm b/ios/chrome/browser/ui/alert_coordinator/modal_alert.mm
new file mode 100644
index 0000000000000000000000000000000000000000..530c89b1e3b71c588b777042246941a9f25c44db
--- /dev/null
+++ b/ios/chrome/browser/ui/alert_coordinator/modal_alert.mm
@@ -0,0 +1,60 @@
+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#import "ios/chrome/browser/ui/alert_coordinator/modal_alert.h"
+
+#import "base/mac/scoped_nsobject.h"
+#include "ui/base/l10n/l10n_util.h"
+#include "ui/strings/grit/ui_strings.h"
+
+@interface ModalAlert () {
+  // Stores the title of the alert.
+  base::scoped_nsobject<NSString> _title;
+}
+
+@end
+
+@implementation ModalAlert
+
+- (instancetype)initWithTitle:(NSString*)title {
+  self = [super init];
+  if (self) {
+    _title.reset([title copy]);
+  }
+  return self;
+}
+
+#pragma mark - Private Methods

[lpromero, 2016/07/18 12:55:31]

s/Private/AlertCoordinatorDelegate

+
+- (BOOL)alertCoordinatorShouldStart:(AlertCoordinator*)alertCoordinator {
+  // Check that the view is still visible on screen, otherwise just return and
+  // don't show the alert.
+  if (![alertCoordinator.baseViewController.view window] &&

[marq (ping after 24h), 2016/07/18 13:02:41]

The coordinator shouldn't need to hand off this check to a delegate, should it?

+      ![alertCoordinator.baseViewController.view
+          isKindOfClass:[UIWindow class]])
+    return NO;
+
+  if ([alertCoordinator actionsCount] == 0) {
+    [alertCoordinator addItemWithTitle:l10n_util::GetNSString(IDS_APP_OK)

[lpromero, 2016/07/18 12:11:36]

Why here and not when creating the UIAlertController?

[gambard, 2016/07/18 12:40:20]

This code adds an OK button only if there is no other button. It is here to
prevent a situation where you display an alert with no button (which the user
cannot dismiss).

[lpromero, 2016/07/18 12:55:31]

I misunderstood the flow with alertCoordinatorUIAlertController:. Ack!

[marq (ping after 24h), 2016/07/18 13:02:41]

I don't like that UI configuration is being done here as a side effect of
-alertCoordinatorShouldStart. Again, can't the coordinator just check this?

[lpromero, 2016/07/18 13:25:19]

The problem is that there are 2 cases we are handling: alert and action sheet
and I guess they don't have the same behavior. This is to separate the code
paths.

[marq (ping after 24h), 2016/07/18 13:37:14]

Yes, but coordinators are allowed to know things about the view controllers they
manage. It can even be abstracted a bit -- if the coordinator is going to
present something using the popover style, then it doesn't care if there are no
actions; otherwise, if there are no actions, it adds an 'OK' item by default. 

+                                action:nil
+                                 style:UIAlertActionStyleDefault];
+  }
+  return YES;
+}
+
+- (UIAlertController*)alertCoordinatorUIAlertController:
+    (AlertCoordinator*)alertCoordinator {
+  UIAlertController* alert =
+      [UIAlertController alertControllerWithTitle:_title
+                                          message:alertCoordinator.message
+                                   preferredStyle:UIAlertControllerStyleAlert];
+  return alert;
+}
+
+- (BOOL)alertCoordinatorShouldAddCancelButton:

[lpromero, 2016/07/18 12:11:36]

Reading the previous methods implementations, should we introduce a
shouldAddOKButtons?

[gambard, 2016/07/18 12:40:20]

No, the OK button is only here if there is no other button.

[lpromero, 2016/07/18 12:55:31]

Acknowledged.

+    (AlertCoordinator*)alertCoordinator {
+  return NO;
+}
+
+@end