Strip trailing linebreaks on paste due to Chrome bug

When pasting into a selected paragraph, or emptying a paragraph Chrome
adds a linebreak. Our paste into empty uses a selected paragraph for
context so the converter picks up this extra linebreak.

It is possible that this breaks are intentional but not likely
so better just to trim than to leave the user with a break which
doesn't even render clearly.

Bug: 58347
Change-Id: Ia6b22cdaeedf1a75bb529c9a5312add9c3ce182c
Merge "Strip trailing linebreaks on paste due to Chrome bug"