Disable subpixel text on linux systems with full_hinting

Disable subpixel text on linux if the system font configuration
specifies full hinting as full hinting doesn't work well with subpixel
text positioning.

BUG=390317
R=derat@chromium.org

Review URL: https://codereview.chromium.org/369673003

git-svn-id: svn://svn.chromium.org/blink/trunk@177439 bbb929c8-8fbe-4397-9dbb-9b2b20218538