[fsp] Add an initial AsyncFileUtil.
This patch adds the AsyncFileUtil implementation for the file system provider.
It does not communicate with the file system provider service yet.
Currently, for not supported operations SECURITY error is returned. For
allowed, but not implemented operations, it is NOT_FOUND error.
Unit tests are quite trivial at this stage, but they will grow once more
operations are implemented.
TEST=unit_test: FileSystemProviderAsyncFileUtilTest*
BUG=248427
Review URL: https://codereview.chromium.org/236303017
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@264462 0039d316-1c4b-4281-b951-d872f2087c98
11 files changed
