Add unittests checking that old saved session can be restored.

ios/web/navigation/serializable_user_data_manager_impl.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.
 
 #import "ios/web/navigation/serializable_user_data_manager_impl.h"
 
 #import "base/mac/foundation_util.h"
 #include "base/memory/ptr_util.h"
 #import "ios/web/public/web_state/web_state.h"
 
@@ skipping 32 matching lines @@
         web_state->GetUserData(kSerializableUserDataManagerKey));
   }
 
   // Returns the manager owned by this wrapper.
   SerializableUserDataManagerImpl* manager() { return &manager_; }
 
  private:
   // The SerializableUserDataManagerWrapper owned by this object.
   SerializableUserDataManagerImpl manager_;
 };
+
+// Returns a dictionary mapping old CRWSessionStorage serialised properties to
+// the corresponding key in the serialised user data. When adding a mapping to
+// this dictionary, create a new crbug to track its removal and mark it with a
+// release at least one year after the introduction of the mapping.
+NSDictionary* GetLegacyKeyConversion() {
+  NSMutableDictionary* legacy_key_conversion = [NSMutableDictionary dictionary];
+  // TODO(crbug.com/661633): those mappings where introduced between M57 and
+  // M58, so remove them after M67 has shipped to stable.
+  [legacy_key_conversion addEntriesFromDictionary:@{
+    @"tabId" : @"TabID",
+    @"openerId" : @"OpenerID",
+    @"openerNavigationIndex" : @"OpenerNavigationIndex",
+    @"lastVisitedTimestamp" : @"LastVisitedTimestamp",
+  }];
+  return [legacy_key_conversion copy];
+}
 }  // namespace
 
 // static
 std::unique_ptr<SerializableUserData> SerializableUserData::Create() {
   return base::MakeUnique<SerializableUserDataImpl>();
 }
 
 SerializableUserDataImpl::SerializableUserDataImpl()
-    : data_(@{}), legacy_key_conversions_(@{
-        @"tabId" : @"TabID",
-        @"openerId" : @"OpenerID",
-        @"openerNavigationIndex" : @"OpenerNavigationIndex",
-        @"lastVisitedTimestamp" : @"LastVisitedTimestamp",
-      }) {}
+    : data_(@{}), legacy_key_conversions_(GetLegacyKeyConversion()) {}
 
 SerializableUserDataImpl::~SerializableUserDataImpl() {}
 
 SerializableUserDataImpl::SerializableUserDataImpl(NSDictionary* data)
     : data_([data copy]) {}
 
 void SerializableUserDataImpl::Encode(NSCoder* coder) {
   [coder encodeObject:data_ forKey:kSerializedUserDataKey];
 }
 
@@ skipping 46 matching lines @@
 void SerializableUserDataManagerImpl::AddSerializableUserData(
     SerializableUserData* data) {
   if (data) {
     SerializableUserDataImpl* data_impl =
         static_cast<SerializableUserDataImpl*>(data);
     data_.reset([data_impl->data() mutableCopy]);
   }
 }
 
 }  // namespace web