Take text path into account when stripping spaces

Take the text path (simple vs complex) into account when computing the
width of a space character used to strip leading and trailing spaces.

R=leviw@chromium.org
BUG=427415
TEST=fast/text/international/complex-text-leading-space-wrapping.html

Review URL: https://codereview.chromium.org/721433002

git-svn-id: svn://svn.chromium.org/blink/trunk@185148 bbb929c8-8fbe-4397-9dbb-9b2b20218538