Remove UnifiedAST memory calculation and clean up instance-creation aspects of UnifiedAST.
This patch is in preparation for pluggable CompilePerms workers.

Patch by: scottb
Review by: bobv


git-svn-id: https://google-web-toolkit.googlecode.com/svn/releases/1.6@4129 8db76d5a-ed1c-0410-87a9-c151d255dfc7