[ios] Disable Undo-Close-All when tab grid is not empty

Undo-Close-All is only valid when the tab grid is empty.
This CL disables the undo action when a tab is added.

Bug: 1112759
Change-Id: I41e407068a227fc87b53be12db8f35329cff52a1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2438233
Commit-Queue: edchin <edchin@chromium.org>
Auto-Submit: edchin <edchin@chromium.org>
Reviewed-by: Sergio Collazos <sczs@chromium.org>
Cr-Commit-Position: refs/heads/master@{#811938}

ios/chrome/browser/ui/tab_grid/tab_grid_view_controller.mm

@@ -1158,6 +1158,10 @@ - (void)gridViewController:(GridViewController*)gridViewController
 
 - (void)gridViewController:(GridViewController*)gridViewController
         didChangeItemCount:(NSUInteger)count {
+  if (count > 0) {
+    // Undo is only available when the tab grid is empty.
+    self.undoCloseAllAvailable = NO;
+  }
   [self configureButtonsForActiveAndCurrentPage];
   if (gridViewController == self.regularTabsViewController) {
     self.topToolbar.pageControl.regularTabCount = count;
@@ -1247,10 +1251,11 @@ - (void)closeAllButtonTapped:(id)sender {
                 self.regularTabsViewController.gridEmpty);
       if (self.undoCloseAllAvailable) {
         [self.regularTabsDelegate undoCloseAllItems];
+        self.undoCloseAllAvailable = NO;
       } else {
         [self.regularTabsDelegate saveAndCloseAllItems];
+        self.undoCloseAllAvailable = YES;
       }
-      self.undoCloseAllAvailable = !self.undoCloseAllAvailable;
       [self configureCloseAllButtonForCurrentPageAndUndoAvailability];
       break;
     case TabGridPageRemoteTabs: