Added web::GetCommittedItemWithUniqueID function.

ios/web/navigation/navigation_manager_util.mm

+// Copyright 2017 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.
+
+#include "ios/web/navigation/navigation_manager_util.h"
+
+#import "ios/web/public/navigation_item.h"
+#import "ios/web/public/navigation_manager.h"
+
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
+namespace web {
+
+NavigationItem* GetCommittedItemWithUniqueID(
+    NavigationManager* navigation_manager,
+    int unique_id) {
+  int index = GetCommittedItemIndexWithUniqueID(navigation_manager, unique_id);
+  return index != -1 ? navigation_manager->GetItemAtIndex(index) : nullptr;
+}
+
+int GetCommittedItemIndexWithUniqueID(NavigationManager* navigation_manager,
+                                      int unique_id) {
+  for (int i = 0; i < navigation_manager->GetItemCount(); i++) {
+    web::NavigationItem* item = navigation_manager->GetItemAtIndex(i);
+    if (item->GetUniqueID() == unique_id) {
+      return i;
+    }
+  }
+  return -1;
+}
+
+}  // namespace web