commit 790103c4b1528189d3dec05fb8cb2138381dbd02
author Dave Borowitz <dborowitz@google.com> Fri Mar 25 14:00:55 2016 -0400
committer Dave Borowitz <dborowitz@google.com> Wed Apr 06 07:31:33 2016 -0400
tree 0e9469700d964acf13fb067b6dd0f5a0f29207b6
parent f71b304786287f376ca8d348e3547e1c814b68b8

Store NoteDb migration state inside Change

Since a ReviewDb write might succeed but its corresponding NoteDb
write might fail, we would like to be able to detect and fix up such
problems after the fact. The most reliable way to do so is to store,
somewhere, the complete set of ref state across the change meta repo
and All-Users for a given Change entity. This effectively needs to
be in Change, or at least in ReviewDb, so that we can write it in the
same transaction that stores the rest of the Change mutation.

Split up NoteDbUpdateManager into two phases, "stage" and "execute".
Stage the change before committing the ReviewDb transaction, and use
the results of staging to update the noteDbState field in Change.

The state is abstracted as an immutable data type NoteDbChangeState,
and NoteDbUpdateManager computes a "Delta" over the type. This
abstraction helps with compile-time safety and testability. However,
for simplicity in the Change record, we just serialize the results
into a simple, parsimonious string.

Change-Id: I2cccda1ccb54062aa1e80ecc82994614ef6d9598