Bug: b/119276649
Merge of http://go/wvgerrit/68903
Test: Android + Linux unit tests
The FileSystem interface as it exists expects an Open for a file and
then a Close when finished. However, the Close doesn't delete the file
itself and depending on the platform, the underlying impl_ as well,
leading to a memory leak. To fix this leak as well as harden against
future memory issues, this change refactors the interface to shift away
from raw pointers and towards smart pointers.
Change-Id: I7a7132ea95cd3775796a540f510b698f4f27dd24
5ec8923b85