Allow cancelling the currently-presented dialog.

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

Index: ios/chrome/browser/ui/dialogs/dialog_presenter.mm
diff --git a/ios/chrome/browser/ui/dialogs/dialog_presenter.mm b/ios/chrome/browser/ui/dialogs/dialog_presenter.mm
index 5be1336d79c6197da14be2bf9134ffb2e13f5a03..812bdf2c834432e8a0bc8e70a4df6af939a62085 100644
--- a/ios/chrome/browser/ui/dialogs/dialog_presenter.mm
+++ b/ios/chrome/browser/ui/dialogs/dialog_presenter.mm
@@ -312,15 +312,23 @@ - (void)runAuthDialogForProtectionSpace:(NSURLProtectionSpace*)protectionSpace
 }
 
 - (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);
   }
 }