Remove NavigationManager::GetPreviousItem().

ios/web/navigation/crw_session_controller.mm

 // Copyright 2012 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/web/navigation/crw_session_controller.h"
 
 #include <stddef.h>
 
 #include <algorithm>
 #include <utility>
@@ skipping 203 matching lines @@
                                     _currentNavigationIndex,
                                     _previousNavigationIndex, _pendingItemIndex,
                                     _entries, _pendingEntry.get(),
                                     _transientEntry.get()];
 }
 
 - (web::NavigationItemList)items {
   return [self itemListForEntryList:self.entries];
 }
 
+- (NSUInteger)itemCount {
+  return self.entries.count;
+}
+
 - (web::NavigationItemImpl*)currentItem {
   return self.currentEntry.navigationItemImpl;
 }
 
 - (web::NavigationItemImpl*)visibleItem {
   return self.visibleEntry.navigationItemImpl;
 }
 
 - (web::NavigationItemImpl*)pendingItem {
   return self.pendingEntry.navigationItemImpl;
@@ skipping 400 matching lines @@
   NSInteger index = _currentNavigationIndex;
   // This will return the first session entry if all other entries are
   // redirects, regardless of the transition state of the first entry.
   while (index > 0 && [self isRedirectTransitionForItemAtIndex:index]) {
     --index;
   }
   return [_entries objectAtIndex:index];
 }
 
 - (NSInteger)indexOfItem:(const web::NavigationItem*)item {
-  web::NavigationItemList items = self.items;
-  for (NSInteger i = 0; i < static_cast<NSInteger>(items.size()); ++i) {
-    if (items[i] == item)
-      return i;
+  for (NSUInteger index = 0; index < self.entries.count; ++index) {
+    if ([self.entries[index] navigationItem] == item)
+      return static_cast<NSInteger>(index);
   }
   return NSNotFound;
 }
 
+- (web::NavigationItemImpl*)itemAtIndex:(NSInteger)index {
+  if (index < 0 || self.entries.count <= static_cast<NSUInteger>(index))
+    return nullptr;
+  return static_cast<web::NavigationItemImpl*>(
+      [self.entries[index] navigationItem]);
+}
+
 #pragma mark -
 #pragma mark Private methods
 
 - (CRWSessionEntry*)sessionEntryWithURL:(const GURL&)url
                                referrer:(const web::Referrer&)referrer
                              transition:(ui::PageTransition)transition
                          initiationType:
                              (web::NavigationInitiationType)initiationType {
   GURL loaded_url(url);
   BOOL urlWasRewritten = NO;
@@ skipping 28 matching lines @@
 }
 
 - (web::NavigationItemList)itemListForEntryList:(NSArray*)entries {
   web::NavigationItemList list(entries.count);
   for (size_t index = 0; index < entries.count; ++index)
     list[index] = [entries[index] navigationItem];
   return list;
 }
 
 @end