Unreviewed ASSERT fix on Chromium bots (in debug).

Unreviewed ASSERT fix on Chromium bots (in debug).

It appears that http://trac.webkit.org/changeset/113031 caused ASSERT in CSSParser::parseFillProperty.
I added the ASSERT to fix the compilation about values not handled in the switch. I supposed the callers
were only property ids handled in the switch case. It wasn't the case, so I'm restoring the old behavior
while keeping the code to compile (it still need a deeper investigation but let fix the bots quickly).

* css/CSSParser.cpp:
(WebCore::CSSParser::parseFillProperty):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@113046 268f45cc-cd09-0410-ab3c-d52691b4dbfc