Remove the concept of currentItemIndex

ios/web/navigation/navigation_manager_impl.mm

Index: ios/web/navigation/navigation_manager_impl.mm
diff --git a/ios/web/navigation/navigation_manager_impl.mm b/ios/web/navigation/navigation_manager_impl.mm
index 8d3ccad5d1c72df4f5f424ea43a86b2aae556e7f..990b93022fff56af22fd1e13e7b1ada599d3f5f8 100644
--- a/ios/web/navigation/navigation_manager_impl.mm
+++ b/ios/web/navigation/navigation_manager_impl.mm
@@ -275,18 +275,14 @@ bool AreURLsInPageNavigation(const GURL& existing_url, const GURL& new_url) {
   return [session_controller_ itemAtIndex:index];
 }
 
-int NavigationManagerImpl::GetCurrentItemIndex() const {
-  return [session_controller_ currentNavigationIndex];
-}
-
 int NavigationManagerImpl::GetPendingItemIndex() const {
   if (GetPendingItem()) {
     if ([session_controller_ pendingItemIndex] != -1) {
       return [session_controller_ pendingItemIndex];
     }
-    // TODO(crbug.com/665189): understand why current item index is
+    // TODO(crbug.com/665189): understand why last committed item index is
     // returned here.
-    return GetCurrentItemIndex();
+    return GetLastCommittedItemIndex();
   }
   return -1;
 }
@@ -369,7 +365,7 @@ bool AreURLsInPageNavigation(const GURL& existing_url, const GURL& new_url) {
 
 int NavigationManagerImpl::GetIndexForOffset(int offset) const {
   int result = [session_controller_ pendingItemIndex] == -1
-                   ? GetCurrentItemIndex()
+                   ? GetLastCommittedItemIndex()
                    : static_cast<int>([session_controller_ pendingItemIndex]);
 
   if (offset < 0) {
@@ -446,7 +442,7 @@ bool AreURLsInPageNavigation(const GURL& existing_url, const GURL& new_url) {
 
 NavigationItem* NavigationManagerImpl::GetLastCommittedNonAppSpecificItem()
     const {
-  int index = GetCurrentItemIndex();
+  int index = GetLastCommittedItemIndex();
   if (index == -1)
     return nullptr;
   WebClient* client = GetWebClient();