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

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

+// 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.
+
+#import "ios/chrome/browser/ui/tab_switcher/tab_model_snapshot.h"
+
+#include "base/strings/sys_string_conversions.h"
+#import "ios/chrome/browser/tabs/tab.h"
+
+TabModelSnapshot::TabModelSnapshot(TabModel* tabModel) {
+  for (Tab* tab in tabModel) {
+    _hashes.push_back(hashOfTheVisiblePropertiesOfATab(tab));
+    _tabs.push_back(base::WeakNSObject<Tab>(tab));
+  }
+}
+
+TabModelSnapshot::~TabModelSnapshot() {}
+
+std::vector<size_t> const& TabModelSnapshot::hashes() const {
+  DCHECK_EQ(_tabs.size(), _hashes.size());
+  return _hashes;
+}
+
+std::vector<base::WeakNSObject<Tab>> const& TabModelSnapshot::tabs() const {
+  DCHECK_EQ(_tabs.size(), _hashes.size());
+  return _tabs;
+}
+
+size_t TabModelSnapshot::hashOfTheVisiblePropertiesOfATab(Tab* tab) {
+  DCHECK(tab);
+  std::stringstream ss;
+  // lastVisitedTimestamp is used as an approximation for whether the tab's
+  // snapshot changed.
+  ss << tab.tabId << std::endl
+     << base::SysNSStringToUTF8(tab.urlDisplayString) << std::endl
+     << std::hexfloat << tab.lastVisitedTimestamp << std::endl;
+  return std::hash<std::string>()(ss.str());
+}