Upstream Chrome on iOS source code [9/11].

ios/chrome/browser/ui/tab_switcher/tab_model_snapshot.h

+// Copyright 2016 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_CHROME_BROWSER_UI_TAB_SWITCHER_TAB_MODEL_SNAPSHOT_H_
+#define IOS_CHROME_BROWSER_UI_TAB_SWITCHER_TAB_MODEL_SNAPSHOT_H_
+
+#import <Foundation/Foundation.h>
+#include <vector>
+
+#import "base/ios/weak_nsobject.h"
+
+@class TabModel;
+@class Tab;
+
+// Contains an approximate snapshot of the tab model passed to the initializer.
+// Used to feed the cells to UICollectionViews, and to compute the changes
+// required to update UICollectionViews.
+// The changes are computed based on a list of hashes of the tabs.
+// One resulting limitation is that there is no differenciation between a tab
+// that is partially updated (because the snapshot changed), and a completely
+// new tab replacing an older tab. This limitation has little impact because
+// very few navigations occur when the tab switcher is shown.
+class TabModelSnapshot {
+ public:
+  // Default constructor. |tabModel| can be nil.
+  explicit TabModelSnapshot(TabModel* tabModel);
+  ~TabModelSnapshot();
+  // Returns the list of hashes for every tabs contained in the TabModel during
+  // the initialization.
+  std::vector<size_t> const& hashes() const;
+  // Returns a list of weak pointers to the tabs.
+  std::vector<base::WeakNSObject<Tab>> const& tabs() const;
+  // Returns a hash of the properties of a tab that are visible in the tab
+  // switcher's UI.
+  static size_t hashOfTheVisiblePropertiesOfATab(Tab* tab);
+
+ private:
+  std::vector<base::WeakNSObject<Tab>> _tabs;
+  std::vector<size_t> _hashes;
+};
+
+#endif  // IOS_CHROME_BROWSER_UI_TAB_SWITCHER_TAB_MODEL_SNAPSHOT_H_