Add kVisible flag to vold::Disk

The new flag is used to indicate that a stub volume (external storage
volume shared with Chrome OS) is visible to Android apps.

Bug: 123377807
Bug: 142684760
Bug: 132796154
Test: Check logcat logs for StorageManagerService.mount() when the
Test: visibility setting of a removable device is toggled in Chrome OS.
Test: Confirm that the visibility setting is properly set.
Test: (Tested in R)
Change-Id: Ica69110d5667837a72a5c8693ff3bccc0f09a82d
2 files changed