Wire up storage stats API to installd.

Wire up storage stats API to installd.

Now that installd has the implementation details we need, we can wire
up the public APIs to use them.

Shuffle APIs around a bit so that StorageStats can be reused for both
UID and UserHandle results, and rename StorageSummary to
ExternalStorageStats.  Provide getTotalBytes() and getFreeBytes() as
first-class methods so we can answer those questions quickly without
paying the cost of measuring external storage details.

Current costs on a typical device with a test account after flushing
dentry caches:

queryStatsForUid() manual: 6922ms
queryStatsForUid() quota: 525ms

queryStatsForUser() manual: 1686ms
queryStatsForUser() quota: 113ms

queryExternalStatsForUser() manual: 42ms
queryExternalStatsForUser() quota: 2ms

For verification purposes, a new "fw.verify_storage" system property
can be set to compute both manual and quota statistics, and log any
discrepancies.

Test: builds, boots
Bug: 27948817, 32206268
Change-Id: I4ea3df3372a7379aa8cf4c20c44120c8f0702c15