This begins splitting up the Deserializer class into
{Object,Partial,Startup}Deserializer.  For now, all functionality remains in
the Deserializer base clase, to be refactored in future CLs.  Empty .cc files
are added here to avoid having to touch build files again.

Bug: v8:6624
Change-Id: If563e03492991bd55c91cd2e09312c0a26aaab2c
Reviewed-on: https://chromium-review.googlesource.com/598067Reviewed-by: Yang Guo <yangguo@chromium.org>
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#47107}