Add support for SubpixelFontScaling flag on windows

Implement support for the SubpixelFontScaling runtime enabled feature
on windows.

BUG=290411
R=pdr@chromium.org

Review URL: https://codereview.chromium.org/25639003

git-svn-id: svn://svn.chromium.org/blink/trunk@158966 bbb929c8-8fbe-4397-9dbb-9b2b20218538