Enable the CSSVariables setting in css-variable-definition.html test
https://bugs.webkit.org/show_bug.cgi?id=116231

Reviewed by Andreas Kling.

CSSVariablesEnabled setting must be set to true to allow
CSSVariables at runtime.

Modified also the indent size to 4 spaces.

* css3/css-variable-definition-expected.html:
* css3/css-variable-definition.html:

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@150184 268f45cc-cd09-0410-ab3c-d52691b4dbfc