[AF Sync] Make storage_key for wallet metadata encode type()

This CL changes the storage_key used for wallet metadata sync bridge.
We need to include the type() in the storage_key because of a difference
between USS and Directory. In USS, DELETE changes are sent from the
server to the bridge without the specifics (that include type()).
Implementing the deletion without knowing the type() would need a hacky
code, to say the least.

It is okay to change the storage_key schema now because this was not
defined before (in Directory) and the USS implementation has not hit any
user, yet.

Bug: 853688
Change-Id: I3d5504855783c089686d613822a49904eb233352
Reviewed-on: https://chromium-review.googlesource.com/c/1403417
Commit-Queue: Jan Krcal <jkrcal@chromium.org>
Reviewed-by: Sebastien Seguin-Gagnon <sebsg@chromium.org>
Cr-Commit-Position: refs/heads/master@{#621512}
4 files changed