Sum up character widths to get the last line width for ellipsis.

To properly apply ellipsis, we virtually concatenate the last line and
overflowed lines after line breaking for a paragraph.
Previously, width of the concatenated line was computed by summing up all
line's width.  However, the width is wrong when there are any trailing
white  spaces that can be normal white spaces by concatenating lines.
With this CL, we sum up widths of all characters in lines except the last
overflowed line.

Bug: 28599066
Change-Id: I41d828ee8eb8a702cd5096d626b307cbb3467047