We switched to our memory-wrapped store everywhere outside the
VE surface, but not in the VE surface itself.
Change the way we construct MemoryStorage objects so that they can
be constructed from a specific mw.SafeStorage instance.
Ensure MemoryStorage's cache is populated with initial storage object
data, and that the cache is copied over when we create derivative
objectes.
Bug: T310438
Change-Id: I652428f114dc5169195887cb8ca719ae196bb76f
