[tab_grid] Hack-in border for active tab.

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

Index: ios/clean/chrome/browser/ui/tab_grid/tab_grid_view_controller.mm
diff --git a/ios/clean/chrome/browser/ui/tab_grid/tab_grid_view_controller.mm b/ios/clean/chrome/browser/ui/tab_grid/tab_grid_view_controller.mm
index dd85b856122b0482f828615ced9c46712e65c261..3400713651ce129499cf3fd8d89cb6fb1e4b85a6 100644
--- a/ios/clean/chrome/browser/ui/tab_grid/tab_grid_view_controller.mm
+++ b/ios/clean/chrome/browser/ui/tab_grid/tab_grid_view_controller.mm
@@ -118,9 +118,18 @@ const CGFloat kToolbarHeight = 64.0f;
   [cell setAppearanceForTabTitle:[self.dataSource titleAtIndex:indexPath.item]
                          favicon:nil
                         cellSize:CGSizeZero];
+  [cell setSelected:(indexPath.item == [self.dataSource indexOfActiveTab])];
   return cell;
 }
 
+#pragma mark - UICollectionViewDelegate methods
+
+- (BOOL)collectionView:(UICollectionView*)collectionView
+    shouldSelectItemAtIndexPath:(NSIndexPath*)indexPath {
+  // Prevent user selection of items.
+  return NO;
+}
+
 #pragma mark - ZoomTransitionDelegate methods
 
 - (CGRect)rectForZoomWithKey:(NSObject*)key inView:(UIView*)view {
@@ -149,6 +158,13 @@ const CGFloat kToolbarHeight = 64.0f;
   NSInteger index = [self.grid numberOfItemsInSection:0];
   NSIndexPath* indexPath = [NSIndexPath indexPathForItem:index inSection:0];
   auto updateBlock = ^{
+    // Unselect current selected item.
+    NSInteger selectedIndex = [self.dataSource indexOfActiveTab];
+    NSIndexPath* selectedIndexPath =
+        [NSIndexPath indexPathForItem:selectedIndex inSection:0];
+    [self.grid reloadItemsAtIndexPaths:@[ selectedIndexPath ]];
+
+    // Create and show new tab.
     [self.tabCommandHandler createNewTabAtIndexPath:indexPath];
     [self.tabCommandHandler showTabAtIndexPath:indexPath];
     [self.grid insertItemsAtIndexPaths:@[ indexPath ]];
@@ -164,7 +180,14 @@ const CGFloat kToolbarHeight = 64.0f;
 }
 
 - (void)cellPressed:(UICollectionViewCell*)cell {
-  [self.tabCommandHandler showTabAtIndexPath:[self.grid indexPathForCell:cell]];
+  NSInteger selectedIndex = [self.dataSource indexOfActiveTab];
+  NSIndexPath* selectedIndexPath =
+      [NSIndexPath indexPathForItem:selectedIndex inSection:0];
+
+  NSIndexPath* newSelectedIndexPath = [self.grid indexPathForCell:cell];
+  [self.tabCommandHandler showTabAtIndexPath:newSelectedIndexPath];
+  [self.grid
+      reloadItemsAtIndexPaths:@[ selectedIndexPath, newSelectedIndexPath ]];
 }
 
 - (void)deleteButtonPressedForCell:(UICollectionViewCell*)cell {