drive: Add ResourceEntry::metadata_edit_state

EntryUpdatePerformer uses this property to detect changes.

BUG=260538
TEST=unit_tests
R=kinaba@chromium.org

Review URL: https://codereview.chromium.org/94693002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@237864 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 237864