Don't clear the forward history when replacing entries.

content/browser/frame_host/navigation_controller_impl.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.
 
 /*
  * Copyright (C) 2006, 2007, 2008, 2009 Apple Inc. All rights reserved.
  * Copyright (C) 2008 Nokia Corporation and/or its subsidiary(-ies)
  * Copyright (C) 2008, 2009 Torch Mobile Inc. All rights reserved.
  *     (http://www.torchmobile.com/)
  *
@@ skipping 1633 matching lines @@
   // need to keep continuity with the pending entry, so copy the pending entry's
   // unique ID to the committed entry. If the pending_entry_index_ isn't -1,
   // then the renderer navigated on its own, independent of the pending entry,
   // so don't copy anything.
   if (pending_entry_ && pending_entry_index_ == -1)
     entry->set_unique_id(pending_entry_->GetUniqueID());
 
   DiscardNonCommittedEntriesInternal();
 
   int current_size = static_cast<int>(entries_.size());
-  DCHECK_IMPLIES(replace, current_size > 0);
+
+  // When replacing, don't prune the forward history.
+  if (replace) {
+    DCHECK_GT(current_size, 0);
+    int32 page_id = entry->GetPageID();
+    entries_[last_committed_entry_index_] = entry.release();
+
+    // This is a new page ID, so we need everybody to know about it.
+    delegate_->UpdateMaxPageID(page_id);
+    return;
+  }
 
   if (current_size > 0) {
     // Prune any entries which are in front of the current entry.
-    // Also prune the current entry if we are to replace the current entry.
     // last_committed_entry_index_ must be updated here since calls to
     // NotifyPrunedEntries() below may re-enter and we must make sure
     // last_committed_entry_index_ is not left in an invalid state.
-    if (replace)
-      --last_committed_entry_index_;
-
     int num_pruned = 0;
     while (last_committed_entry_index_ < (current_size - 1)) {
       num_pruned++;
       entries_.pop_back();
       current_size--;
     }
     if (num_pruned > 0)  // Only notify if we did prune something.
       NotifyPrunedEntries(this, false, num_pruned);
   }
 
@@ skipping 322 matching lines @@
     }
   }
 }
 
 void NavigationControllerImpl::SetGetTimestampCallbackForTest(
     const base::Callback<base::Time()>& get_timestamp_callback) {
   get_timestamp_callback_ = get_timestamp_callback;
 }
 
 }  // namespace content