drive: Add drive/trash

This directory is used to hold locally deleted entries which are waiting for server side deletion.
search_metadata.cc looks up parent entries to know if each entry is under the trash or not.

BUG=260542
TEST=unit_tests
R=kinaba@chromium.org

Review URL: https://codereview.chromium.org/82673003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@237044 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 237044