Expect two tabs in StartupSupervisedUserProfile test on Windows 10.

chrome/browser/ui/startup/startup_browser_creator_browsertest.cc

Index: chrome/browser/ui/startup/startup_browser_creator_browsertest.cc
diff --git a/chrome/browser/ui/startup/startup_browser_creator_browsertest.cc b/chrome/browser/ui/startup/startup_browser_creator_browsertest.cc
index bbfb604470af57542d1bfd02f8dab3e344b8f220..e5a280543a0d81a9e7706cb24b359618d88ae3db 100644
--- a/chrome/browser/ui/startup/startup_browser_creator_browsertest.cc
+++ b/chrome/browser/ui/startup/startup_browser_creator_browsertest.cc
@@ -1187,8 +1187,9 @@ IN_PROC_BROWSER_TEST_F(SupervisedUserBrowserCreatorTest,
   ASSERT_TRUE(new_browser);
 
   TabStripModel* tab_strip = new_browser->tab_strip_model();
-  // There should be only one tab.
-  EXPECT_EQ(1, tab_strip->count());
+  // There should be only one tab, except on Windows 10. See crbug.com/505029.
+  const int tab_count = IsWindows10OrNewer() ? 2 : 1;
+  EXPECT_EQ(tab_count, tab_strip->count());
 }
 
 #endif  // !defined(OS_CHROMEOS)