Moved TabID implementation to SerializableUserData.

ios/web/navigation/serializable_user_data_manager_impl.h

 // 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.
 
 #ifndef IOS_WEB_NAVIGATION_SERIALIZABLE_USER_DATA_MANAGER_IMPL_H_
 #define IOS_WEB_NAVIGATION_SERIALIZABLE_USER_DATA_MANAGER_IMPL_H_
 
 #import "base/mac/scoped_nsobject.h"
 #import "ios/web/public/serializable_user_data_manager.h"
 
 namespace web {
 
 class SerializableUserDataImpl : public SerializableUserData {
  public:
   SerializableUserDataImpl();
   ~SerializableUserDataImpl();
 
   // Constructor taking the NSDictionary holding the serializable data.
   explicit SerializableUserDataImpl(NSDictionary* data);
 
   // SerializableUserData:
   void Encode(NSCoder* coder) override;
   void Decode(NSCoder* coder) override;
 
   // Returns the serializable data.
   NSDictionary* data() { return data_; };
 
  private:
+  // Decodes the values that were previously encoded using CRWSessionStorage's
+  // NSCoding implementation and returns an NSDictionary using the new
+  // serialization keys.
+  // TODO(crbug.com/691800): Remove legacy support.
+  NSDictionary* GetDecodedLegacyValues(NSCoder* coder);
+
   // The dictionary passed on initialization.  After calling Decode(), this will
   // contain the data that is decoded from the NSCoder.
   base::scoped_nsobject<NSDictionary> data_;
+  // Some values that were previously persisted directly in CRWSessionStorage
+  // are now serialized using SerializableUserData, and this dictionary is used
+  // to decode these values. The keys are the legacy encoding keys, and the
+  // values are their corresponding serializable user data keys.
+  base::scoped_nsobject<NSDictionary> legacy_key_conversions_;
 };
 
 class SerializableUserDataManagerImpl : public SerializableUserDataManager {
  public:
   SerializableUserDataManagerImpl();
   ~SerializableUserDataManagerImpl();
 
   // SerializableUserDataManager:
   void AddSerializableData(id<NSCoding> data, NSString* key) override;
   id<NSCoding> GetValueForSerializationKey(NSString* key) override;
   std::unique_ptr<SerializableUserData> CreateSerializableUserData()
       const override;
   void AddSerializableUserData(SerializableUserData* data) override;
 
  private:
   // The dictionary that stores serializable user data.
   base::scoped_nsobject<NSMutableDictionary> data_;
 };
 
 }  // namespace web
 
 #endif  // IOS_WEB_NAVIGATION_SERIALIZABLE_USER_DATA_MANAGER_IMPL_H_