Add support in generate scripts to handle Conditional

WEB_AUDIO and SVG_FONTS conditions in tagName files were 
handled by generate scripts and this CL adds the support. 
This fix was also needed to build without SVG_FONTS enabled.

Review URL: https://codereview.chromium.org/330093002

git-svn-id: svn://svn.chromium.org/blink/trunk@176249 bbb929c8-8fbe-4397-9dbb-9b2b20218538