Don't update export button if export flag is disabled

This CL fixes a bug that causes a crash when the export feature is disabled.

Bug: 789122, 814574
Cq-Include-Trybots: master.tryserver.chromium.mac:ios-simulator-cronet;master.tryserver.chromium.mac:ios-simulator-full-configs
Change-Id: I19bca436ff86cb93b7b2fea786e8e4dfcb9dd4b9
Reviewed-on: https://chromium-review.googlesource.com/941123Reviewed-by: Sylvain Defresne <sdefresne@chromium.org>
Commit-Queue: Ioana Pandele <ioanap@chromium.org>
Cr-Commit-Position: refs/heads/master@{#539848}

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

@@ -632,15 +632,21 @@ void SavePasswordsConsumer::OnGetPasswordStoreResults(
   [super collectionViewWillBeginEditing:collectionView];
 
   [self setSavePasswordsSwitchItemEnabled:NO];
-  [self setExportPasswordsButtonEnabled:NO];
+  if (base::FeatureList::IsEnabled(
+          password_manager::features::kPasswordExport)) {
+    [self setExportPasswordsButtonEnabled:NO];
+  }
 }
 
 - (void)collectionViewWillEndEditing:(UICollectionView*)collectionView {
   [super collectionViewWillEndEditing:collectionView];
 
   [self setSavePasswordsSwitchItemEnabled:YES];
-  if (exportReady_) {
-    [self setExportPasswordsButtonEnabled:YES];
+  if (base::FeatureList::IsEnabled(
+          password_manager::features::kPasswordExport)) {
+    if (exportReady_) {
+      [self setExportPasswordsButtonEnabled:YES];
+    }
   }
 }