DocumentsUI: Fix the issue of download status was displayed incompletely

The layout arrangement of date, size and summary are unreasonable.
Text was ellipsized when summary has too much characters.

Reconfigure "layout_weight" of date, size and summary can fix this
issue.

CRs-Fixed: 619201

Change-Id: I0c00d08d4793a38b80988378b4b510bdb3bf8720