Remove usage of GetActiveEntry [1/n]

This CL is part of a serie of CL to remove usage of the deprecated
method NavigationController::GetActiveEntry.

Bug: 273710
Change-Id: I179116d10ad8894ad0c88112cea519641dc240ae
Reviewed-on: https://chromium-review.googlesource.com/1102457
Commit-Queue: Dominic Mazzoni <dmazzoni@chromium.org>
Reviewed-by: Dominic Mazzoni <dmazzoni@chromium.org>
Cr-Commit-Position: refs/heads/master@{#567649}

chrome/browser/accessibility/interstitial_accessibility_browsertest.cc

@@ -65,11 +65,7 @@ IN_PROC_BROWSER_TEST_F(InterstitialAccessibilityBrowserTest,
 
   // Ensure that we got an interstitial page.
   ASSERT_FALSE(web_contents->IsCrashed());
-  content::NavigationEntry* entry =
-      web_contents->GetController().GetActiveEntry();
-  ASSERT_TRUE(entry);
-  EXPECT_TRUE(entry->GetPageType() == content::PAGE_TYPE_ERROR ||
-              entry->GetPageType() == content::PAGE_TYPE_INTERSTITIAL);
+  EXPECT_TRUE(web_contents->ShowingInterstitialPage());
 
   // Now check from the perspective of accessibility - we should be focused
   // on a page with title "Privacy error". Keep waiting on accessibility