drive: Add RemovePerformer

RemovePerformer is basically RemoveOperation without cache file removing code and OnDirectoryChangedByOperation() notification.

RemovePerformer::DeleteResource performs normal delete.
RemovePerformer::UnparentResource handles special case for shared_with_me entries.

Offline delete will be done in steps shown below:
 1. RemoveOperation removes local cache file, moves the local metadata entry to drive/trash, and notifies OnDirectoryChangedByOperation() event.
 2. SyncClient notices the change (via new OperationObserver event).
 3. RemovePerformer requests server to delete the entry, removes the local metadata entry.

BUG=260542
TEST=unit_tests --gtest_filter="RemovePerformerTest.*"
R=kinaba@chromium.org

Review URL: https://codereview.chromium.org/68413002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@234350 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 234350