Connect Mojo budget_service to BudgetManager implementation of Reserve.

This connects the Mojo service to the pre-existing implementation of
Reserve. It also updates the Reserve implementation to track both whether
the origin had enough budget to spend as well as whether there was an
error in reading or writing the database. Tests were updated to reflect
the new parameters, but no new tests were needed.

BUG=617971

Review-Url: https://codereview.chromium.org/2326523003
Cr-Commit-Position: refs/heads/master@{#418244}
7 files changed