Fix getVolumeInfo for files.

This patch fixes getVolumeInfo to work with files. Previously, it was incorrectly detecting each FileEntry as a fake entry.

Along the way, the util.isFakeDirectoryEntry has been removed, since fakes are always directories, so we can use util.isFakeEntry instead.

TEST=Tested manually.
BUG=326925

Review URL: https://codereview.chromium.org/110073002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@239482 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 239482