Clean up setting font-family: initial value.

Most of the code there was no-ops.

R=eae,eseidel
BUG=

Review URL: https://codereview.chromium.org/204963002

git-svn-id: svn://svn.chromium.org/blink/trunk@169582 bbb929c8-8fbe-4397-9dbb-9b2b20218538
[CSS Shapes] shape-outside: ellipse(50% 50% at) causes crash

The BasicShape ellipse and circle functions now report a syntax error
if the "at" keyword is not followed by a position.

The existing parsing tests have been updated to include this case.

Ported over from http://trac.webkit.org/changeset/165835

BUG=353774

Review URL: https://codereview.chromium.org/203413006

git-svn-id: svn://svn.chromium.org/blink/trunk@169583 bbb929c8-8fbe-4397-9dbb-9b2b20218538