Fix/deflake tests in /chrome/browser/unload_browsertest.cc.

This is a prerequisite for switching WindowedNotificationObserver to use
base::RunLoop instead of deprecated MessageLoopRunner.

This CL is split out from https://crrev.com/c/982612.

This CL was uploaded by git cl split.

R=alexmos@chromium.org

Bug: 668707
Change-Id: I2d723e7938ac7e07c6334e58b26b60e7e493834e
Reviewed-on: https://chromium-review.googlesource.com/1120487Reviewed-by: Alex Moshchuk <alexmos@chromium.org>
Commit-Queue: Alexander Semashko <ahest@yandex-team.ru>
Cr-Commit-Position: refs/heads/master@{#571661}

chrome/browser/unload_browsertest.cc

@@ -149,10 +149,15 @@ class UnloadTestBase : public InProcessBrowserTest {
         base::Bind(&chrome_browser_net::SetUrlRequestMocksEnabled, true));
   }
 
-  void CheckTitle(const char* expected_title) {
+  void CheckTitle(const char* expected_title, bool wait = false) {
+    auto* web_contents = browser()->tab_strip_model()->GetActiveWebContents();
     base::string16 expected = base::ASCIIToUTF16(expected_title);
-    EXPECT_EQ(expected,
-              browser()->tab_strip_model()->GetActiveWebContents()->GetTitle());
+    base::string16 actual;
+    if (wait)
+      actual = content::TitleWatcher(web_contents, expected).WaitAndGetTitle();
+    else
+      actual = web_contents->GetTitle();
+    EXPECT_EQ(expected, actual);
   }
 
   void NavigateToDataURL(const char* html_content, const char* expected_title) {
@@ -633,15 +638,13 @@ IN_PROC_BROWSER_TEST_P(UnloadTest, BrowserCloseTabWhenOtherTabHasListener) {
   content::WindowedNotificationObserver observer(
         chrome::NOTIFICATION_TAB_ADDED,
         content::NotificationService::AllSources());
-  content::WindowedNotificationObserver load_stop_observer(
-      content::NOTIFICATION_LOAD_STOP,
-      content::NotificationService::AllSources());
   content::SimulateMouseClick(
       browser()->tab_strip_model()->GetActiveWebContents(), 0,
       blink::WebMouseEvent::Button::kLeft);
   observer.Wait();
-  load_stop_observer.Wait();
-  CheckTitle("popup");
+  // Need to wait for the title, because the initial page (about:blank) can stop
+  // loading before the click handler calls document.write.
+  CheckTitle("popup", true);
 
   content::WebContentsDestroyedWatcher destroyed_watcher(
       browser()->tab_strip_model()->GetActiveWebContents());