Adds a new switch for enabling the new local server backend.
Actually two flags which play in tandem:
--enable-local-sync-backend and --local-sync-backend-dir
The second is respected only if the first one is specified.
Eventually those will be controlled by policy but the flags will allow
easier testing and potentially unlock the feature for advanced users.
For now sign-in is needed to kick the sync logic on but the data
is only stored locally when this flag is specified.
BUG=651411
TEST=unit_tests/manual.
Review-Url: https://codereview.chromium.org/2442453002
Cr-Commit-Position: refs/heads/master@{#429280}
17 files changed
