Make drag&drop be atomic for undo/redo.

For undo/redo, drag&drop is recorded as a 2 operations, paste and
delete. This CL makes drag&drop be atomic operation to be properly
undoed/redoed.

Bug: 27268820
Change-Id: Ia38d663f046c2c65f348985934f5cfa054b0437e
2 files changed