Initialize all CSSParserValue's variables

The isInt variable of CSSParserValue was often not initialized in CSSGrammar.y.
This CL fixes that.

BUG=385386

Review URL: https://codereview.chromium.org/340503002

git-svn-id: svn://svn.chromium.org/blink/trunk@176323 bbb929c8-8fbe-4397-9dbb-9b2b20218538