Bring back delay for auto-drawing drawer.

We keep auto-closing for drawer as user hover away, but bringing back
delay for opening. This is to prevent drawer opening by accident as user
operates in multi-window mode, i.e. move a file from the right window to
the left window.

Bug: 34736674
Change-Id: I7714dc074ad137797b05be5ec18762ffc82f66fa