Remove NavigationManager::GetPreviousItem().

ios/web/navigation/crw_session_controller.mm

Index: ios/web/navigation/crw_session_controller.mm
diff --git a/ios/web/navigation/crw_session_controller.mm b/ios/web/navigation/crw_session_controller.mm
index ca244ef94b99814bda5c65a1ae3e7f8c14b5d1e7..a7d0b3ef6dd8b9f8d969a64f9e4ae2a7e9d23691 100644
--- a/ios/web/navigation/crw_session_controller.mm
+++ b/ios/web/navigation/crw_session_controller.mm
@@ -220,6 +220,10 @@
   return [self itemListForEntryList:self.entries];
 }
 
+- (NSUInteger)itemCount {
+  return [self.entries count];

[Eugene But (OOO till 7-30), 2017/03/02 23:32:48]

nit: self.entries.count 

|count| is a property

+}
+
 - (web::NavigationItemImpl*)currentItem {
   return self.currentEntry.navigationItemImpl;
 }
@@ -641,14 +645,20 @@
 }
 
 - (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 i = 0; i < [self.entries count]; ++i) {

[Eugene But (OOO till 7-30), 2017/03/02 23:32:48]

ditto

+    if ([self.entries[i] navigationItem] == item)
+      return static_cast<NSInteger>(i);
   }
   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