Move code for checking file extensions and MIME types from
ExternalStorageProvider into android.os.FileUtils, so it can be used by
other clients (e.g. DownloadsProvider).
BUG=20157955
Change-Id: Ib16a16af723c21fb8d2912c8917dfd68653ea6fa
When creating or renaming files on external storage, sanitize the
requested display names to be valid FAT filenames. This also fixes
a handful of directory traversal bugs.
Also relax logic around generating display names to allow any
extension which maps to the requested MIME type. Tests to verify.
Bug: 18512473, 18504132
Change-Id: I89e632019ee145f53d9d9d2050932f8939a756af