Change Font::codePath to check TextRenderingMode

Change the Font::codePath implementation to also check the
TextRenderingMode when determining the appropriate code path to be
used. This fixes a bug where preferred width would be computed using
the simple code path and the actual text layout using the complex
code path.

R=dglazkov@chromium.org
BUG=415087
TEST=fast/text/sub-pixel/complex-text-preferred-width.html

Review URL: https://codereview.chromium.org/590923002

git-svn-id: svn://svn.chromium.org/blink/trunk@182874 bbb929c8-8fbe-4397-9dbb-9b2b20218538