DocumentsUI: Fix 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: Ic2db20a303dd1db7e2d3375e4b733d704daf393b