Load permissions and usages concurrently.

Now that the two loaders do not conflict, we can load them at the same
time.  This speeds up the loading of the usage graph, which used to
have to wait for the permissions to be loaded to start.

Test: Open ManageStandardPermissionsFragment.
Change-Id: Id4d9d31f80a6714f514d8a126294528d0442f1ff