Reland "Rename FontItalics to FontStyle to match CSS terminology"

Rename the FontItalics enum, the FontDescription italics/
setItalics methods and wrappers to FontStyle, style and style
respectively to better match the CSS terminology.

TBR=zmo@chromium.org
BUG=

Review URL: https://codereview.chromium.org/200763004

git-svn-id: svn://svn.chromium.org/blink/trunk@169278 bbb929c8-8fbe-4397-9dbb-9b2b20218538