Add confirmation for passwords export

This alerts the user about exporting passwords and allows them to confirm the action or cancel it.

Bug: 789122
Cq-Include-Trybots: master.tryserver.chromium.mac:ios-simulator-cronet;master.tryserver.chromium.mac:ios-simulator-full-configs
Change-Id: I84af89eae3c5b7004d197826abf1a1f5eccc3bb6
Reviewed-on: https://chromium-review.googlesource.com/817418Reviewed-by: Sylvain Defresne <sdefresne@chromium.org>
Commit-Queue: Ioana Pandele <ioanap@chromium.org>
Cr-Commit-Position: refs/heads/master@{#523825}

ios/chrome/app/strings/ios_strings.grd

@@ -1072,6 +1072,12 @@ Handoff must also be enabled in the General section of Settings, and your device
       <message name="IDS_IOS_EXPORT_PASSWORDS" desc="Button that the user can press to export passwords. [Length: 22em] [iOS only]">
         Export Passwords...
       </message>
+      <message name="IDS_IOS_EXPORT_PASSWORDS_ALERT_MESSAGE" desc="The message of the alert displayed as a warning to the user who tapped on the button to export passwords. [iOS only]">
+        Your passwords will be visible to anyone who can see the exported file. Do not share this file with anyone.
+      </message>
+      <message name="IDS_IOS_EXPORT_PASSWORDS_CANCEL_BUTTON" desc="Label of a confirmation dialog button which allows the user to cancel passwords export. [Length: 22em] [iOS only]">
+        Cancel
+      </message>
       <message name="IDS_IOS_SAVE_PASSWORDS_MANAGE_ACCOUNT" desc="Header text with link for the view in Settings for managing saved passwords. [Length: unlimited] [iOS only]">
         View and manage saved passwords at <ph name="BEGIN_LINK">BEGIN_LINK</ph>passwords.google.com<ph name="END_LINK">END_LINK</ph>
       </message>

ios/chrome/browser/ui/settings/save_passwords_collection_view_controller.mm

@@ -4,6 +4,8 @@
 
 #import "ios/chrome/browser/ui/settings/save_passwords_collection_view_controller.h"
 
+#import <UIKit/UIKit.h>
+
 #include "base/ios/ios_util.h"
 #include "base/logging.h"
 #include "base/mac/foundation_util.h"
@@ -148,9 +150,14 @@ void SavePasswordsConsumer::OnGetPasswordStoreResults(
   // Module containing the reauthentication mechanism for viewing and copying
   // passwords.
   ReauthenticationModule* reauthenticationModule_;
+  // Boolean containing whether the export button and functionality are enabled
+  // or not.
+  BOOL exportEnabled_;
 }
+
 // Kick off async request to get logins from password store.
 - (void)getLoginsFromPasswordStore;
+
 @end
 
 @implementation SavePasswordsCollectionViewController
@@ -470,9 +477,36 @@ void SavePasswordsConsumer::OnGetPasswordStoreResults(
     exportPasswordsItem_.textColor = [[MDCPalette greyPalette] tint500];
     exportPasswordsItem_.accessibilityTraits = UIAccessibilityTraitNotEnabled;
     [self reconfigureCellsForItems:@[ exportPasswordsItem_ ]];
+    exportEnabled_ = NO;
+  } else {
+    exportEnabled_ = YES;
   }
 }
 
+- (void)startPasswordsExportFlow {
+  UIAlertController* exportConfirmation = [UIAlertController
+      alertControllerWithTitle:nil
+                       message:l10n_util::GetNSString(
+                                   IDS_IOS_EXPORT_PASSWORDS_ALERT_MESSAGE)
+                preferredStyle:UIAlertControllerStyleActionSheet];
+  UIAlertAction* cancelAction =
+      [UIAlertAction actionWithTitle:l10n_util::GetNSString(
+                                         IDS_IOS_EXPORT_PASSWORDS_CANCEL_BUTTON)
+                               style:UIAlertActionStyleCancel
+                             handler:nil];
+  [exportConfirmation addAction:cancelAction];
+
+  // TODO(crbug.com/789122): Ask for password serialization
+  // and wire re-authentication.
+  UIAlertAction* exportAction = [UIAlertAction
+      actionWithTitle:l10n_util::GetNSString(IDS_IOS_EXPORT_PASSWORDS)
+                style:UIAlertActionStyleDefault
+              handler:nil];
+  [exportConfirmation addAction:exportAction];
+
+  [self presentViewController:exportConfirmation animated:YES completion:nil];
+}
+
 #pragma mark UICollectionViewDelegate
 
 - (void)openDetailedViewForForm:(const autofill::PasswordForm&)form {
@@ -518,10 +552,13 @@ void SavePasswordsConsumer::OnGetPasswordStoreResults(
       [self openDetailedViewForForm:*blacklistedForms_[indexPath.item]];
       break;
     case ItemTypeExportPasswordsButton:
+      DCHECK_EQ(SectionIdentifierExportPasswordsButton,
+                [model sectionIdentifierForSection:indexPath.section]);
       DCHECK(base::FeatureList::IsEnabled(
           password_manager::features::kPasswordExport));
-      // TODO(crbug.com/789122): Trigger alert dialogue to confirm passwords
-      // export.
+      if (exportEnabled_) {
+        [self startPasswordsExportFlow];
+      }
       break;
     default:
       NOTREACHED();