Add DCHECKs for invariants on NavigationController indices.

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 516 matching lines @@
   const std::string& mime_type = delegate_->GetContentsMimeType();
   bool is_viewable_mime_type =
       mime_util::IsSupportedNonImageMimeType(mime_type) &&
       !media::IsSupportedMediaMimeType(mime_type);
   NavigationEntry* visible_entry = GetVisibleEntry();
   return visible_entry && !visible_entry->IsViewSourceMode() &&
       is_viewable_mime_type && !delegate_->GetInterstitialPage();
 }
 
 int NavigationControllerImpl::GetLastCommittedEntryIndex() const {
+  // The last committed entry index must always be less than the number of
+  // entries.  It should be -1 iff there are no entries.
+  DCHECK_LT(last_committed_entry_index_, GetEntryCount());
+  DCHECK_EQ(last_committed_entry_index_ == -1, GetEntryCount() == 0);
   return last_committed_entry_index_;
 }
 
 int NavigationControllerImpl::GetEntryCount() const {
-  DCHECK(entries_.size() <= max_entry_count());
+  DCHECK_LE(entries_.size(), max_entry_count());
   return static_cast<int>(entries_.size());
 }
 
 NavigationEntryImpl* NavigationControllerImpl::GetEntryAtIndex(
     int index) const {
   if (index < 0 || index >= GetEntryCount())
     return nullptr;
 
   return entries_[index].get();
 }
@@ skipping 1167 matching lines @@
   DiscardNonCommittedEntriesInternal();
 
   // If there was a transient entry, invalidate everything so the new active
   // entry state is shown.
   if (transient) {
     delegate_->NotifyNavigationStateChanged(INVALIDATE_TYPE_ALL);
   }
 }
 
 NavigationEntryImpl* NavigationControllerImpl::GetPendingEntry() const {
+  // If there is no pending_entry_, there should be no pending_entry_index_.
+  DCHECK(pending_entry_ || pending_entry_index_ == -1);
+
+  // If there is a pending_entry_index_, then pending_entry_ must be the entry
+  // at that index.
+  DCHECK(pending_entry_index_ == -1 ||
+         pending_entry_ == GetEntryAtIndex(pending_entry_index_));
+
   return pending_entry_;
 }
 
 int NavigationControllerImpl::GetPendingEntryIndex() const {
+  // The pending entry index must always be less than the number of entries.
+  // If there are no entries, it must be exactly -1.
+  DCHECK_LT(pending_entry_index_, GetEntryCount());
+  DCHECK(GetEntryCount() != 0 || pending_entry_index_ == -1);
   return pending_entry_index_;
 }
 
 void NavigationControllerImpl::InsertOrReplaceEntry(
     std::unique_ptr<NavigationEntryImpl> entry,
     bool replace) {
   DCHECK(!ui::PageTransitionCoreTypeIs(entry->GetTransitionType(),
                                        ui::PAGE_TRANSITION_AUTO_SUBFRAME));
 
   // If the pending_entry_index_ is -1, the navigation was to a new page, and we
@@ skipping 412 matching lines @@
     }
   }
 }
 
 void NavigationControllerImpl::SetGetTimestampCallbackForTest(
     const base::Callback<base::Time()>& get_timestamp_callback) {
   get_timestamp_callback_ = get_timestamp_callback;
 }
 
 }  // namespace content