[SyncFS] Add folder reorganization testing functions to FakeDriveServiceHelper.

BUG=331988

Review URL: https://codereview.chromium.org/136003004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@247212 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 247212