Floats following inlines break to next line unncessarily

Don't include trailing space in linewidth calculations when deciding
if a float can fit on a line.

Merge http://trac.webkit.org/changeset/148622

Review URL: https://codereview.chromium.org/343663004

git-svn-id: svn://svn.chromium.org/blink/trunk@177135 bbb929c8-8fbe-4397-9dbb-9b2b20218538