Cleanup of how -enableDesktopUserAgent uses NavigationManager utility.

ios/chrome/browser/web/navigation_manager_util_unittest.mm

 // Copyright 2017 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #import "ios/chrome/browser/web/navigation_manager_util.h"
 
 #import "ios/web/public/navigation_item.h"
 #import "ios/web/public/test/fakes/test_navigation_manager.h"
 #include "testing/gtest/include/gtest/gtest.h"
 #import "testing/gtest_mac.h"
 #include "testing/platform_test.h"
 #include "ui/base/page_transition_types.h"
 #include "url/gurl.h"
 
 class NavigationManagerUtilTest : public PlatformTest {
  protected:
   web::TestNavigationManager nav_manager_;
 };
 
 // Tests that empty navigation manager returns nullptr.
 TEST_F(NavigationManagerUtilTest, TestLastNonRedirectedItemEmpty) {
+  EXPECT_FALSE(GetLastNonRedirectedItem(nullptr));
   EXPECT_FALSE(GetLastNonRedirectedItem(&nav_manager_));
 }
 
 // Tests that typed in URL works correctly.
 TEST_F(NavigationManagerUtilTest, TestLastNonRedirectedItemTypedUrl) {
   nav_manager_.AddItem(GURL("http://foo.com/page0"), ui::PAGE_TRANSITION_TYPED);
   web::NavigationItem* item = GetLastNonRedirectedItem(&nav_manager_);
   ASSERT_TRUE(item);
   EXPECT_TRUE(ui::PageTransitionTypeIncludingQualifiersIs(
       item->GetTransitionType(), ui::PAGE_TRANSITION_TYPED));
@@ skipping 42 matching lines @@
   nav_manager_.AddItem(GURL("http://foo.com/page0"), ui::PAGE_TRANSITION_TYPED);
   nav_manager_.AddItem(GURL("http://bar.com/redir1"),
                        ui::PAGE_TRANSITION_CLIENT_REDIRECT);
   nav_manager_.AddItem(GURL("http://bar.com/redir2"),
                        ui::PAGE_TRANSITION_CLIENT_REDIRECT);
   web::NavigationItem* item = GetLastNonRedirectedItem(&nav_manager_);
   ASSERT_TRUE(item);
   EXPECT_TRUE(ui::PageTransitionTypeIncludingQualifiersIs(
       item->GetTransitionType(), ui::PAGE_TRANSITION_TYPED));
 }