Force --enable-webkit-text-subpixel-positioning for DSF > 1.0.

We already do this for fonts in the UI, and we should also do this for fonts in
the actual web content (i.e. everywhere where chromium falls back on an
operating system font, e.g. when specifying just “monospace”).

before this change:
http://t.zekjur.net/2015-03-21-003244_2357x1809_scrot.png

after this change:
http://t.zekjur.net/2015-03-21-003308_2357x1775_scrot.png

BUG=396659,143619

Review URL: https://codereview.chromium.org/1020263004

Cr-Commit-Position: refs/heads/master@{#323085}
4 files changed