Add parseFontFaceDescriptor for @font-face handling

Add parseFontFaceDescriptor for @font-face handling, similar to
parseViewportProperty. Change FontFace to make it
end up in this new code path too.

With this change using initial/inherit/unset on properties
in @font-face is not possible anymore and all properties
not handled in parseFontFaceProperty are discarded.

This also addresses bug 408484, i.e. using !important
in @font-face causes the property to be dropped.

Behavior matches FireFox.

BUG=404023, 408484

Review URL: https://codereview.chromium.org/1103273010

git-svn-id: svn://svn.chromium.org/blink/trunk@194903 bbb929c8-8fbe-4397-9dbb-9b2b20218538
7 files changed