Fix trailing space handling for complex text

Fix bug in line layout where it was incorrectly assumed that trailing
spaces would always be measured with the simple font code path.

R=chrishtr@chromium.org
BUG=423274
TEST=fast/text/international/complex-text-trailing-space.html

Review URL: https://codereview.chromium.org/655073002

git-svn-id: svn://svn.chromium.org/blink/trunk@183716 bbb929c8-8fbe-4397-9dbb-9b2b20218538