Fix "Crash after closing last tab twice" bug.

Call |contentWillAppearAnimated| on the tab grid view controller before
dispatch_async.

Bug: 1134718, 1134062
Change-Id: Id8c61f596bdf69371f9b126e671d621eac54dbd8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2449349Reviewed-by: Gauthier Ambard <gambard@chromium.org>
Commit-Queue: Roberto Moura <mouraroberto@google.com>
Auto-Submit: Roberto Moura <mouraroberto@google.com>
Cr-Commit-Position: refs/heads/master@{#814596}

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

@@ -186,8 +186,8 @@
     // This is done with a dispatch to make sure that the view isn't added to
     // the view hierarchy right away, as it is not the expectations of the
     // API.
+    [self.baseViewController contentWillAppearAnimated:animated];
     dispatch_async(dispatch_get_main_queue(), ^{
-      [self.baseViewController contentWillAppearAnimated:animated];
       self.baseViewController.childViewControllerForStatusBarStyle = nil;
 
       self.transitionHandler = [[TabGridTransitionHandler alloc]