Supervised user interstitial: Don't destroy WebContents that might still be in use

chrome/browser/supervised_user/supervised_user_browsertest.cc

Index: chrome/browser/supervised_user/supervised_user_browsertest.cc
diff --git a/chrome/browser/supervised_user/supervised_user_browsertest.cc b/chrome/browser/supervised_user/supervised_user_browsertest.cc
index bbe40e0e4965b74e2f5cf90981b17d681314dc00..10dfdcd5dd836eb18a38b6ae3e874b364efc6d8d 100644
--- a/chrome/browser/supervised_user/supervised_user_browsertest.cc
+++ b/chrome/browser/supervised_user/supervised_user_browsertest.cc
@@ -214,9 +214,12 @@ IN_PROC_BROWSER_TEST_F(SupervisedUserBlockModeTest, OpenBlockedURLInNewTab) {
   // On pressing the "back" button, the new tab should be closed, and we should
   // get back to the previous active tab.
   MockTabStripModelObserver observer(tab_strip);
+  base::RunLoop run_loop;
   EXPECT_CALL(observer,
-              TabClosingAt(tab_strip, tab, tab_strip->active_index()));
+              TabClosingAt(tab_strip, tab, tab_strip->active_index()))
+      .WillOnce(testing::InvokeWithoutArgs(&run_loop, &base::RunLoop::Quit));
   GoBack(tab);
+  run_loop.Run();
   EXPECT_EQ(prev_tab, tab_strip->GetActiveWebContents());
 }