Measure external storage using new GIDs.

Measure external storage using new GIDs.

We just defined a new range of GIDs that will be used to mark per-app
data files stored on external storage, so start measuring them.

Also measure all OBB files using another new GID that was defined.

Note that we're relying on the per-app cache GIDs to track cache
usage on *both* internal and external storage, which means that stats
and extStats won't always add up.  (The framework already combines
these values together, and we didn't want to waste precious GID
space on explicitly tracking cache files on external storage.)

Test: builds, boots
Bug: 27948817, 34263266
Change-Id: Ife087df299ff8ee1a75fce1e39b4b737cf9375d5