Use custom user data to serialize Tab last visited timestamp.

ios/web/navigation/crw_session_controller.mm

 // Copyright 2012 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/web/navigation/crw_session_controller.h"
 
 #include <stddef.h>
 
 #include <algorithm>
 #include <utility>
@@ skipping 44 matching lines @@
 
   // The transient entry, if any. A transient entry is discarded on any
   // navigation, and is used for representing interstitials that need to be
   // represented in the session.  It backs the property of the same name and
   // should only be set through its setter.
   base::scoped_nsobject<CRWSessionEntry> _transientEntry;
 
    // Stores the certificate policies decided by the user.
   CRWSessionCertificatePolicyManager* _sessionCertificatePolicyManager;
 
-  // The timestamp of the last time this tab is visited, represented in time
-  // interval since 1970.
-  NSTimeInterval _lastVisitedTimestamp;
-
   // The browser state associated with this CRWSessionController;
   web::BrowserState* _browserState;  // weak
 
   // Time smoother for navigation entry timestamps; see comment in
   // navigation_controller_impl.h
   web::TimeSmoother _timeSmoother;
 }
 
 // Redefine as readwrite.
 @property(nonatomic, readwrite, assign) NSInteger currentNavigationIndex;
@@ skipping 26 matching lines @@
 // Returns a NavigationItemList containing the NavigationItems from |entries|.
 - (web::NavigationItemList)itemListForEntryList:(NSArray*)entries;
 @end
 
 @implementation CRWSessionController
 
 @synthesize currentNavigationIndex = _currentNavigationIndex;
 @synthesize previousNavigationIndex = _previousNavigationIndex;
 @synthesize pendingItemIndex = _pendingItemIndex;
 @synthesize entries = _entries;
-@synthesize lastVisitedTimestamp = _lastVisitedTimestamp;
 @synthesize openedByDOM = _openedByDOM;
 @synthesize sessionCertificatePolicyManager = _sessionCertificatePolicyManager;
 
 - (instancetype)initWithBrowserState:(web::BrowserState*)browserState
                          openedByDOM:(BOOL)openedByDOM {
   self = [super init];
   if (self) {
     _openedByDOM = openedByDOM;
     _browserState = browserState;
     _entries = [NSMutableArray array];
-    _lastVisitedTimestamp = [[NSDate date] timeIntervalSince1970];
     _currentNavigationIndex = -1;
     _previousNavigationIndex = -1;
     _pendingItemIndex = -1;
     _sessionCertificatePolicyManager =
         [[CRWSessionCertificatePolicyManager alloc] init];
   }
   return self;
 }
 
 - (instancetype)initWithBrowserState:(web::BrowserState*)browserState
@@ skipping 12 matching lines @@
     }
     self.currentNavigationIndex = currentIndex;
     // Prior to M34, 0 was used as "no index" instead of -1; adjust for that.
     if (![_entries count])
       self.currentNavigationIndex = -1;
     if (_currentNavigationIndex >= static_cast<NSInteger>(items.size())) {
       self.currentNavigationIndex = static_cast<NSInteger>(items.size()) - 1;
     }
     _previousNavigationIndex = -1;
     _pendingItemIndex = -1;
-    _lastVisitedTimestamp = [[NSDate date] timeIntervalSince1970];
     _sessionCertificatePolicyManager =
         [[CRWSessionCertificatePolicyManager alloc] init];
   }
   return self;
 }
 
 - (id)copyWithZone:(NSZone*)zone {
   CRWSessionController* copy = [[[self class] alloc] init];
   copy->_openedByDOM = _openedByDOM;
   copy->_currentNavigationIndex = _currentNavigationIndex;
   copy->_previousNavigationIndex = _previousNavigationIndex;
   copy->_pendingItemIndex = _pendingItemIndex;
-  copy->_lastVisitedTimestamp = _lastVisitedTimestamp;
   copy->_entries =
       [[NSMutableArray alloc] initWithArray:_entries copyItems:YES];
   copy->_sessionCertificatePolicyManager =
       [_sessionCertificatePolicyManager copy];
   return copy;
 }
 
 - (void)setCurrentNavigationIndex:(NSInteger)currentNavigationIndex {
   if (_currentNavigationIndex != currentNavigationIndex) {
     _currentNavigationIndex = currentNavigationIndex;
@@ skipping 24 matching lines @@
   }
 }
 
 - (void)setBrowserState:(web::BrowserState*)browserState {
   _browserState = browserState;
   DCHECK(!_navigationManager ||
          _navigationManager->GetBrowserState() == _browserState);
 }
 
 - (NSString*)description {
-  return [NSString
-      stringWithFormat:@"last visit: %f\ncurrent index: %" PRIdNS
-                       @"\nprevious index: %" PRIdNS
-                       @"\npending index: %" PRIdNS
-                       @"\n%@\npending: %@\ntransient: %@\n",
-                       _lastVisitedTimestamp, _currentNavigationIndex,
-                       _previousNavigationIndex, _pendingItemIndex, _entries,
-                       _pendingEntry.get(), _transientEntry.get()];
+  return [NSString stringWithFormat:@"current index: %" PRIdNS
+                                    @"\nprevious index: %" PRIdNS
+                                    @"\npending index: %" PRIdNS
+                                    @"\n%@\npending: %@\ntransient: %@\n",
+                                    _currentNavigationIndex,
+                                    _previousNavigationIndex, _pendingItemIndex,
+                                    _entries, _pendingEntry.get(),
+                                    _transientEntry.get()];
 }
 
 - (web::NavigationItemList)items {
   return [self itemListForEntryList:self.entries];
 }
 
 - (web::NavigationItemImpl*)currentItem {
   return self.currentEntry.navigationItemImpl;
 }
 
@@ skipping 461 matching lines @@
 }
 
 - (web::NavigationItemList)itemListForEntryList:(NSArray*)entries {
   web::NavigationItemList list(entries.count);
   for (size_t index = 0; index < entries.count; ++index)
     list[index] = [entries[index] navigationItem];
   return list;
 }
 
 @end