drive: Make DownloadOperation aware of locally created files

Store an empty file to the cache when the entry is locally created one.

BUG=260539
TEST=unit_tests
R=kinaba@chromium.org

Review URL: https://codereview.chromium.org/132883010

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@247434 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 247434