Fix synthetics when ENABLE_GDI_FONTS_ON_WINDOWS=0.

Fake bold and fake italic are not applied to webfonts when using
Skia on Windows.

BUG=301816

Review URL: https://codereview.chromium.org/25309002

git-svn-id: svn://svn.chromium.org/blink/trunk@158564 bbb929c8-8fbe-4397-9dbb-9b2b20218538