[iOS] Stop coordinators before deallocating them

These coordinators were just being set to nil, without stopping. They
should be stopped first.

Change-Id: If1a1ffb632176c77b9d5d69655f0e9a4f2a3874c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2544464Reviewed-by: Mark Cogan <marq@chromium.org>
Commit-Queue: Robbie Gibson <rkgibson@google.com>
Cr-Commit-Position: refs/heads/master@{#828209}

ios/chrome/browser/ui/browser_view/browser_view_controller.mm

@@ -1570,8 +1570,11 @@ NSString* const kBrowserViewControllerSnackbarCategory =
     self.typingShield = nil;
     if (_voiceSearchController)
       _voiceSearchController->SetDispatcher(nil);
+    [self.primaryToolbarCoordinator stop];
     self.primaryToolbarCoordinator = nil;
+    [self.secondaryToolbarContainerCoordinator stop];
     self.secondaryToolbarContainerCoordinator = nil;
+    [self.secondaryToolbarCoordinator stop];
     self.secondaryToolbarCoordinator = nil;
     self.toolbarInterface = nil;
     [_toolbarUIUpdater stopUpdating];