Adds web::NavigationItem.

This is the web/ analogue of content's NavigationEntry, intended
for use on iOS because iOS cannot depend on content.
NavigationItem captures all the data required to recreate a
browsing state, such as URL, title, and transition type.

BUG=422033
TEST=None

Review URL: https://codereview.chromium.org/647543002

Cr-Commit-Position: refs/heads/master@{#299093}

ios/web/DEPS

+include_rules = [
+  "+ui",
+]

ios/web/ios_web.gyp

@@ -17,6 +17,7 @@
         '../../base/base.gyp:base',
       ],
       'sources': [
+        'public/navigation_item.h',
         'public/user_agent.h',
         'public/user_agent.mm',
       ],

ios/web/public/navigation_item.h

+// Copyright 2014 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.
+
+#ifndef IOS_WEB_PUBLIC_NAVIGATION_ITEM_H_
+#define IOS_WEB_PUBLIC_NAVIGATION_ITEM_H_
+
+#include "base/strings/string16.h"
+#include "ui/base/page_transition_types.h"
+
+class GURL;
+
+namespace web {
+
+// A NavigationItem is a data structure that captures all the information
+// required to recreate a browsing state. It represents one point in the
+// chain of navigation managed by a NavigationManager.
+class NavigationItem {
+ public:
+  virtual ~NavigationItem() {}
+
+  // The actual URL of the page. For some about pages, this may be a scary
+  // data: URL or something like that. Use GetVirtualURL() below for showing to
+  // the user.
+  virtual const GURL& GetURL() const = 0;
+
+  // The URL that should be shown to the user. In most cases this is the same
+  // as the URL above, but in some case the underlying URL might not be
+  // suitable for display to the user.
+  virtual const GURL& GetVirtualURL() const = 0;
+
+  // The title as set by the page. This will be empty if there is no title set.
+  // The caller is responsible for detecting when there is no title and
+  // displaying the appropriate "Untitled" label if this is being displayed to
+  // the user.
+  virtual const base::string16& GetTitle() const = 0;
+
+  // The transition type indicates what the user did to move to this page from
+  // the previous page.
+  virtual ui::PageTransition GetTransitionType() const = 0;
+};
+
+}  // namespace web
+
+#endif  // IOS_WEB_PUBLIC_NAVIGATION_ITEM_H_