Allow cancelling the currently-presented dialog.

ios/chrome/browser/ui/dialogs/dialog_presenter.mm

 // Copyright 2015 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/dialogs/dialog_presenter.h"
 
 #include <deque>
 #include <map>
 
 #import "base/ios/block_types.h"
@@ skipping 294 matching lines @@
       addTextFieldWithConfigurationHandler:^(UITextField* textField) {
         textField.placeholder = l10n_util::GetNSString(
             IDS_IOS_HTTP_LOGIN_DIALOG_PASSWORD_PLACEHOLDER);
         textField.secureTextEntry = YES;
       }];
 
   [self addDialogCoordinator:alertCoordinator forWebState:webState];
 }
 
 - (void)cancelDialogForWebState:(web::WebState*)webState {
-  DCHECK_NE(webState, self.presentedDialogWebState);
-  AlertCoordinator* dialogToCancel = _dialogCoordinatorsForWebStates[webState];
-  if (dialogToCancel) {
+  BOOL cancelingPresentedDialog = webState == self.presentedDialogWebState;
+  AlertCoordinator* dialogToCancel =
+      cancelingPresentedDialog ? self.presentedDialogCoordinator
+                               : _dialogCoordinatorsForWebStates[webState];
+  DCHECK(!cancelingPresentedDialog || dialogToCancel);
+  [dialogToCancel executeCancelHandler];
+  [dialogToCancel stop];
+
+  if (cancelingPresentedDialog) {

[rohitrao (ping after 24h), 2017/06/12 23:43:50]

Should we DCHECK(_dialogCoordinatorsForWebStates[webState] == NULL)?

[kkhorimoto, 2017/06/13 00:10:13]

Done.

+    // Simulate a button tap to trigger showing the next dialog.

[rohitrao (ping after 24h), 2017/06/12 23:43:50]

Can a single WebState have multiple dialogs queued up?  Is it possible for this
line to show *another* dialog for the same |webState|?

[kkhorimoto, 2017/06/13 00:10:13]

This class was built on the assumption that it was not possible.  JavaScript
execution is halted until the dialog is dismissed and the WebKit completion
handler is executed, so only one would be displayed at a time.

+    [self buttonWasTappedForCoordinator:dialogToCancel];

[rohitrao (ping after 24h), 2017/06/12 23:43:50]

It feels a little weird to call a function with this name from here.  Maybe we
should pull what we need out into a helper function?

[kkhorimoto, 2017/06/13 00:10:13]

I renamed it to |-dialogCoordinatorWasStopped:|, which is more accurate.

+  } else if (dialogToCancel) {
+    // Clean up queued state.
     auto it =
         std::find(_queuedWebStates.begin(), _queuedWebStates.end(), webState);
     DCHECK(it != _queuedWebStates.end());
     _queuedWebStates.erase(it);
-    [dialogToCancel executeCancelHandler];
-    [dialogToCancel stop];
     _dialogCoordinatorsForWebStates.erase(webState);
   }
 }
 
 - (void)cancelAllDialogs {
   [self.presentedDialogCoordinator executeCancelHandler];
   [self.presentedDialogCoordinator stop];
   self.presentedDialogCoordinator = nil;
   self.presentedDialogWebState = nil;
   while (!_queuedWebStates.empty()) {
@@ skipping 165 matching lines @@
                                         style:UIAlertActionStyleDestructive];
     [confirmationCoordinator addItemWithTitle:l10n_util::GetNSString(IDS_CANCEL)
                                        action:cancelHandler
                                         style:UIAlertActionStyleCancel];
     [weakSelf setBlockingConfirmationCoordinator:confirmationCoordinator];
     [[weakSelf blockingConfirmationCoordinator] start];
   } copy];
 }
 
 @end