Moved TabID implementation to SerializableUserData.

ios/web/navigation/serializable_user_data_manager_impl.h

Index: ios/web/navigation/serializable_user_data_manager_impl.h
diff --git a/ios/web/navigation/serializable_user_data_manager_impl.h b/ios/web/navigation/serializable_user_data_manager_impl.h
index 38fa1fb1c6402eef9bf6ef2602fc7d75256912b6..029e7f6edb6fd6efbfe31a14a150bceeef72b2b0 100644
--- a/ios/web/navigation/serializable_user_data_manager_impl.h
+++ b/ios/web/navigation/serializable_user_data_manager_impl.h
@@ -29,6 +29,16 @@ class SerializableUserDataImpl : public SerializableUserData {
   // 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_;

[Eugene But (OOO till 7-30), 2017/02/13 17:37:57]

Do we need to set a milestone when we drop support for legacy keys?

[kkhorimoto, 2017/02/13 23:41:18]

Done.

+
+  // Decodes the values that were previously encoded using CRWSessionStorage's
+  // NSCoding implementation and returns an NSDictionary using the new
+  // serialization keys.
+  NSDictionary* GetDecodedLegacyValues(NSCoder* coder);

[Eugene But (OOO till 7-30), 2017/02/13 17:37:57]

Do you want to move method higher (before ivars)?

[kkhorimoto, 2017/02/13 23:41:18]

Done.

 };
 
 class SerializableUserDataManagerImpl : public SerializableUserDataManager {