Remove PropertyType argument for CSSPropertyParser::ImplicitScope

The ImplicitScope is only used with an PropertyImplicit argument, so
there's no need to have this argument at all.

BUG=404023

Review URL: https://codereview.chromium.org/499223002

git-svn-id: svn://svn.chromium.org/blink/trunk@180865 bbb929c8-8fbe-4397-9dbb-9b2b20218538