drive: Rename UpdateOperation to ContentUpdatePerformer

Dirty file upload can be handled as a sub-task of EntryUpdatePerformer.
This class should be put in drive/sync directory.

Move UpdateOperation in file_system to sync and rename it to ContentUpdatePerformer.

BUG=260539
TEST=unit_tests

Review URL: https://codereview.chromium.org/140323006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@246054 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 246054