Followup comments from r460581.

content/browser/frame_host/render_frame_host_manager_unittest.cc

 // Copyright 2013 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.
 
 #include "content/browser/frame_host/render_frame_host_manager.h"
 
 #include <stdint.h>
 
 #include <tuple>
 #include <utility>
@@ skipping 1246 matching lines @@
   rfh1->GetSiteInstance()->IncrementActiveFrameCount();
 
   contents()->NavigateAndCommit(kUrl2);
   TestRenderFrameHost* rfh2 = main_test_rfh();
   rfh2->GetSiteInstance()->IncrementActiveFrameCount();
 
   // Now go back, but suppose the SwapOut_ACK isn't received.  This shouldn't
   // happen, but we have seen it when going back quickly across many entries
   // (http://crbug.com/93427).
   contents()->GetController().GoBack();
-  contents()->GetMainFrame()->PrepareForCommit();
 
   // The back navigation commits.
   const NavigationEntry* entry1 = contents()->GetController().GetPendingEntry();
   contents()->GetPendingMainFrame()->SendNavigate(
       entry1->GetUniqueID(), false, entry1->GetURL());
   EXPECT_TRUE(rfh2->IsWaitingForUnloadACK());
   EXPECT_FALSE(rfh2->is_active());
 
   // We should be able to navigate forward.
   contents()->GetController().GoForward();
@@ skipping 1873 matching lines @@
   ASSERT_FALSE(delete_observer.deleted());
   EXPECT_FALSE(initial_rfh->is_active());
 
   // The initial RFH receives a DidStartProvisionalLoad IPC. It should not
   // create a NavigationHandle.
   initial_rfh->SimulateNavigationStart(kUrl3);
   EXPECT_FALSE(initial_rfh->navigation_handle());
 }
 
 }  // namespace content