Wait for Cryptohome service to be available on login.

chrome/browser/chromeos/login/existing_user_controller_browsertest.cc

Index: chrome/browser/chromeos/login/existing_user_controller_browsertest.cc
diff --git a/chrome/browser/chromeos/login/existing_user_controller_browsertest.cc b/chrome/browser/chromeos/login/existing_user_controller_browsertest.cc
index 9566108f335e2168c4539d03ed31b47dfdbb643b..facc5e4afd1a6ecfb3a0fd816fffb3bee3cb80fb 100644
--- a/chrome/browser/chromeos/login/existing_user_controller_browsertest.cc
+++ b/chrome/browser/chromeos/login/existing_user_controller_browsertest.cc
@@ -784,6 +784,11 @@ class ExistingUserControllerActiveDirectoryTest
     ExistingUserControllerTest::SetUpInProcessBrowserTestFixture();
   }
 
+  void TearDownOnMainThread() override {
+    base::RunLoop().RunUntilIdle();
+    ExistingUserControllerTest::TearDownOnMainThread();
+  }
+
  protected:
   void ExpectLoginFailure() {
     EXPECT_CALL(*mock_login_display_, SetUIEnabled(false)).Times(2);