Re-installing experimental natives after deserialization causes failures if
said experimental native is already included in the snapshot. However, there
is no way to tell whether a certain harmony feature has been included.

Experimental natives may also be turned on/off on-demand, which a snapshot
that includes them would not support for all cases.

The simple solution for the meantime is to never include experimental natives
in the snapshot and initialize them after deserialization on-demand.

R=vogelheim@chromium.org

Review URL: https://codereview.chromium.org/981473002

Cr-Commit-Position: refs/heads/master@{#26982}