[tab_grid] Hack-in new tab FAB action.

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 6296bbe1925abe2f6e98119c66f8d4de537d3fcc..7c365fbcb7998ab208498c8057f871634dd87da1 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
@@ -145,6 +145,19 @@ const CGFloat kToolbarHeight = 64.0f;
   [self.tabGridCommandHandler showTabGrid];
 }
 
+- (void)createNewTab:(id)sender {
+  // PLACEHOLDER: The new WebStateList data structure will have implications
+  // on how new tabs are created.
+  NSInteger index = [self.grid numberOfItemsInSection:0];
+  NSIndexPath* indexPath = [NSIndexPath indexPathForItem:index inSection:0];
+  auto updateBlock = ^{
+    [self.tabCommandHandler createNewTabAtIndexPath:indexPath];
+    [self.tabCommandHandler showTabAtIndexPath:indexPath];
+    [self.grid insertItemsAtIndexPaths:@[ indexPath ]];
+  };
+  [self.grid performBatchUpdates:updateBlock completion:nil];
+}
+
 #pragma mark - SessionCellDelegate
 
 - (TabSwitcherCache*)tabSwitcherCache {